[massive store] Reintroduce methods that are necessary to properly handle master/slave configuration Related to #15538303

[massive store] Follow configuration of the metadata generator Don't drop constraints and indexes for tables that are ignored by the metadata generator given to the store. One may now easily disable insertion of e.g. created_by / owned_by by removing them from the MetadataGenerator.META_RELATIONS set, in which case indexes for associated table won't be removed by the massive store.

[dataimport] make MetadataGenerator.META_RELATIONS customizable This should be done on the instance rather than on the class

[massive store] Rework constraint/index handling The basic idea is to keep the primary constraint on entities.eid since it's heavily used in metadata insertions. Other option would have been to drop / recreate but its very costly on big database, and the index is used for insertion into the entities table itself, so it's not worth droping it at a first glance. Also, keeping it avoids to systematically drop all constraints which depends on it. We may thus now lazily drop constraints, only on insertion of some etype/rtype for the related table. Related to #15538359

[massive store] Lazy removal of constraints and metadata indexes They should not be removed during store's init, because we may want to query the database with its index between store creation and call to prepare_insert* (e.g. to build the extid2eid map). Along the way: * rename drop_metadata_constraints into drop_metadata_indexes, because that's what it does * rework a bit impacted tests Closes #15538359

[repository] Drop the index on entities.type It should be now only used in maintenance queries in checkintegrity. Those are not worth maintaining it. Closes #15538317

[source] Drop source mapping handling It was only used by the cwxmlparser which has been deleted. This is too complex for litle benefit, we don't want to maintain that in cubicweb.

[repository] Drop the entities.extid column and associated cache This was not necessary anymore with promoted usage of the new data import API. Turn repository's _type_extid_cache to _type_cache with only the entity's type as key. This introduces an backward incompatible change: entity_metas dict doesn't contains anymore the extid key, but it doesn't seem used at all anywhere, so this sounds acceptable. Closes #15538317

[repository] Drop the entities.asource column It not used anymore thanks to previous patches. Closes #15538288

[integrity check] Stop using entities.asource column in integrity checks Simply check if entities have a cw_source, and link it to the system source when not found. Related to #15538288

[rql2sql/test] Ensure test results predictability Without this, test were randomly failing within tox due to different order of solutions.

[rql2sql] Stop generating SQL query from RQL using entities.type This was necessary in the "true multi-sources" time, it's not anymore, while maintaining this index is costly. Related to #15538317

[test] Remove some usages of lgc.testlib

[test] Avoid pytest discovery warnings Having TestServerConfiguration and alike in the test module namespace causes pytest discovery errors, because it thinks it's a test class.

flake8 and all * update some copyright * drop most __docformat__ declaration * fix some flake8 warnings / errors

[schema2sql] Drop deprecated comment

[cnx] Use entity_type instead of entity_metas()['type'] The latter is deprecated in favor of the former which has been introduced on cnx to replace it.

[entity] Reimplement and deprecate entity.cw_metainformation It shouldn't rely anymore on cnx.entity_metas which is itself deprecated, and the cw_metainformation API is similarly not needed anymore, access directly to cwuri / cw_source if needed. Related to #15538288

[repository] Drop type_and_source_from_eid and rename related cache We don't want to handle anymore the entities.asource column so we shouldn't use those anymore. Also rename repository's _type_source_cache into _type_extid_cache as this is what it's containing now. Do similar renaming to the system source API. Related to #15538288

[entity] Stop returning source information in cw_metainformation() We should not need that. It has been introduced to handle things we should not do and probably don't do anymore (e.g. attempting to grasp recursive import of several sites). Related to #15538288.

[json] Stop serializing cw_source into default json representation of an entity Related to #15538288

Drop deprecated LDAP related script both are relying on the 'entities.source' column which has been dropped in 3.19. They have been written with the old ldapsource in mind, which has been dropped at that time.

[entity] Stop linking to external site for external entities This behaviour was ok when we had "true" multi-sources but its rather painful with datafeed sources. Also, it makes absolute_url() costlier than what it should. Besides, it relies on cw_metainformation()['source'] that is pending for removal. Instead, add a link to the original object in the metadata view (the one that displays eid and source at the bottom right corner of the primary view). Related to #15538288.

[datafeed] Drop entity deletion handling in the default source / parser This should be handled by specific parser to avoid using "entities.asource". Reimplement it in the ldap parser. Related to #15538288