Missing cross-references for OMERO properties

[sbesson]

Noticed while working on #2433, the cross-references for the OMERO properties are currently broken. Looking at the historical releases, this regression seems to have introduced during the migration to readthedocs.
For instance, compare the omero.ldap.base markup in https://docs.openmicroscopy.org/omero/5.6.4/sysadmins/server-ldap.html vs https://omero.readthedocs.io/en/v5.6.5/sysadmins/server-ldap.html.

The relevant logic is in

omero-documentation/omero/conf.py

Lines 407 to 411 in 72fa9fe

	app.add_crossref_type(
	directivename = "property",
	rolename = "property",
	indextemplate = "%s",
	)

There are a few factors that might have caused this regression but the two obvious ones coming to mind are:

1- change in newer Sphinx major version (5.6.4 was built with Sphinx 3 vs Sphinx 5 for 5.6.5)
2- self-hosted vs readthedocs infrastructure.

[sbesson]

After much troubleshooting, I finally identified the source of the problem which is a collision between the custom property cross-reference defined in conf.py and the property directive of the Python domain.

#2508 is one way to fix this issue by changing the default domain and namespacing all the Python directives/roles wherever appropriate. Another approach would be to modify our our custom prefix to use a non-colliding name like omeroproperty, omeroconfig or similar. The second strategy would be a larger change that would modify many pages of the documentation and require modifications to omero config parse and thus I decide to start the discussion with the less intrusive approach.