[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.

### Requirements for tests in various cubicweb/**/test directories. ###

## shared by several test folders
cubicweb-card
docutils
Twisted < 16.0.0
webtest

## cubicweb/test
Pygments
mock
#fyzz XXX pip install fails
cubicweb-file
cubicweb-localperms
cubicweb-tag

## cubicweb/devtools/test
flake8

## cubicweb/hooks/test
psycopg2

## cubicweb/pyramid/test
pyramid >= 1.5.0
waitress >= 0.8.9
wsgicors >= 0.3
pyramid_multiauth

## cubicweb/sobject/test
cubicweb-comment