Switch default domain to the reStructuredText domain

[sbesson]

Fixes #2434

See https://www.sphinx-doc.org/en/master/usage/configuration.html#confval-primary_domain and https://www.sphinx-doc.org/en/master/usage/domains/index.html

The definition of a custom property cross-reference clashes with the directive defined in the Python domain which is the default domain. To fix the usage without updating all references, this changes the default domain to rst and updates all directives, roles and references specific to the Python domain in the table documentation page to use the py namespace

The definition of the custom property cross-reference is also amended to use an indextemplate value consistent with the reference documentation

In terms of testing:

• check there are no changes to the configuration properties page i.e. https://omero--2508.org.readthedocs.build/en/2508/sysadmins/config.html vs https://omero.readthedocs.io/en/stable/sysadmins/config.html
• check the pages with references to OMERO configuration properties now link back to the configuration section e.g. https://omero--2508.org.readthedocs.build/en/2508/sysadmins/server-ldap.html vs https://omero.readthedocs.io/en/stable/sysadmins/server-ldap.html
• check the rendering/links in the OMERO.tables page is unaffected https://omero.readthedocs.io/en/stable/developers/Tables.html#omero.grid.Table vs https://omero--2508.org.readthedocs.build/en/2508/developers/Tables.html#omero.grid.Table

[pwalczysko]

In terms of testing:

* check there are no changes to the configuration properties page i.e. https://omero--2508.org.readthedocs.build/en/2508/sysadmins/config.html vs https://omero.readthedocs.io/en/stable/sysadmins/config.html

* check the pages with references to OMERO configuration properties now link back to the configuration section e.g. https://omero--2508.org.readthedocs.build/en/2508/sysadmins/server-ldap.html vs https://omero.readthedocs.io/en/stable/sysadmins/server-ldap.html

* check the rendering/links in the OMERO.tables page is unaffected https://omero.readthedocs.io/en/stable/developers/Tables.html#omero.grid.Table vs https://omero--2508.org.readthedocs.build/en/2508/developers/Tables.html#omero.grid.Table

Test 1: (changes in the configureation properties page):

• Click on the View page source on the two highlighted links and copy the content into two files (2805pr and stable)
• Run diff on those two files
• No changes detected -> pass

Test 2: (references to OMERO configuration properties now link back to the configuration section)

• Click on the omero.ldap.base inside https://omero--2508.org.readthedocs.build/en/2508/sysadmins/server-ldap.html -> note that this is a link which brings you to the config page
• Click on omero.ldap.base inside https://omero.readthedocs.io/en/stable/sysadmins/server-ldap.html -> nothing happens, this is not a link
• Change from no-link to working-link detected -> pass

Test 3: (check the rendering/links in the OMERO.tables page)

• Check optically the htmls -> layout of complex Notes with code, links on the page and internal anchors behaviour
• Note there are no differences between the 2508 and the stable htmls -> pass

[pwalczysko]

Based on testing in #2508 (comment) lgtm. Thank you.