[dataimport] enhance a bit sql queries readability

[dataimport] use IF EXISTS when possible it's better than try/except and avoid potential concurrency problems.

[dataimport] PGHelper should be responsible to retrieve the database schema

[dataimport] introduce a new MetadataGenerator to replace former MetaGenerator with a similar-but-different API that will allow its usage by the massive store (no more entity object manipulation), while making it a bit more flexible for customization by subclasses (experience taken from client code). Related to #10338621

[dataimport] Prefer now(pytz.utc) to utcnow

[dataimport] rename nohook store .source attribute so it's clearly not the samething as metagenerator.source. Also add a bit of doc along the way.

[dataimport] make rql store test easier to read and test a few more thing, then reuse it to test nohook start which had no tests at all

[dataimport] remove useless assignment in massive store

[dataimport] move eid attribution from the metagenerator back to the nohook store

[dataimport] rephrase minor bits of the meta generator

[pkg] Depends on logilab-common >= 1.2.2

Merge with 3.22.3

[pkg] Depends on yams >= 0.43 RPM spec file and debian/control got updated previously.

Added tag 3.22.3, debian/3.22.3-1, centos/3.22.3-1 for changeset b1e7de000536

[pkg] Version 3.22.3

[pkg] Depends on yams < 0.43

Define BASE_URL and DATA_URL js variables in the login template. Closes #13385185 Those are expected to be defined in almost every js files. They were not before this patch because login form doesn't use the regular main template.

[web] Remove some unused imports in editforms

Fix cancel action on deletion confirmation form Currently crashed with RequestError: invalid action '__action_cancel'. It's broken as of https://hg.logilab.org/master/cubicweb/rev/cb217b2b3 This fix is similar as the one done in https://hg.logilab.org/master/cubicweb/rev/9f1c89e7426d Closes #13521493

[rql2sql] Test and fix some case of sql generation when an unstable variable (ie whose type change from one solution to another) is used in an EXISTS node but belongs to an outer scope. Closes #13518646.

[test] Add missing os import in unittest_migractions.py Dropped in ^ merge.

backport 3.22 changes

[entity] Make it possible to specify sorting terms in cw_related_rqlst method Closes #12306543.

[sql gen] Properly create UNIQUE index on non string column. Closes #13728492 Unique was previously detected in a loop triggered only for String columns.