Update .doctrine-project.json for 2.15

[GromNaN]

• Update the current branch to 2.15
• Add version 3.0 as work as started.
• Remove all versions older than 2 years

Reason:

• Algolia has no unlimitied space for indices and creating indices
• Some newer versions got rst fixes that are missing in older versions (because unmaintained and upmerge PITA) that cause at least warnings/notices during the build
• We can remove quick-fixes or centralized solutions in the website code at some point that were done because of older project version docs