[BC break] Move doctrine/cache to optional dependencies

[GromNaN]

Q	A
Type	improvement
BC Break	yes
Fixed issues	#2762 (comment)

Summary

doctrine/cache is deprecated and archived.

Motivation for introducing a breaking change:

• When installing doctrine/mongodb-odm with composer, you get a message even if doctrine/cache is not actively used.

Package doctrine/cache is abandoned, you should avoid using it. No replacement was suggested.

• The next major version will require PHP 8.4.

This is a breaking change only when calling Configuration::getMetadataCacheImpl(). The workaround is easy: add doctrine/cache as project dependency.

I consider projects that use doctrine/cache directly without explicitly requiring the package to be in error.

That's why I'm adding a conflict with doctrine/mongodb-odm-bundle < 5, which did not have an explicit dependency but used the Doctrine\Common\Cache classes:
https://github.com/doctrine/DoctrineMongoDBBundle/blob/48c29009c24ff74c47782c0c9c2736f1f5fd9b0e/DependencyInjection/DoctrineMongoDBExtension.php#L14-L15

[greg0ire]

The quick fix and the proper fix should probably be mentioned in an upgrade guide.