Merge all schema files to have a unique schema file per manifest version

[willdurand]

To fix bugs like #4367, one approach was to generate two sets of schemas (for the two manifest versions we currently support). This was a bit complex and involved a lot of code changes but that's still something we want to do.

Once this has been done (i.e. we have two sets of schema files, see: #4512), we'll want to merge all the schema files to have 1 schema file per manifest version. After that, we'll probably attempt to prune this file to (1) have a structure that really benefits the linter and (2) only keep the relevant information we need in the linter.

┆Issue is synchronized with this Jira Task