Disable old media field GraphQL fields by default.

[gvkries]

OrchardCMS#15003 introduced a new GraphQL type files to group all media item properties together. However, the old fields were left intact, resulting in duplicated fields. This PR removes the old fields by default but provides a compatibility switch to restore them if needed.

As suggested by @sebastienros, I added an AppContext switch to handle this. However, this is the first time we're using an AppContext switch, as far as I can tell. We may need to discuss whether this is the best approach or if we should consider an alternative.

/cc @MikeAlhayek @Piedone @hyzx86

[github-actions]

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