CollectionDocs: filter out doc_fragments and module_utils

[himdel]

Fixes https://issues.redhat.com/browse/AAH-53

This alters the result of both CollectionsAPI.list (each item in the .data.data list) and CollectionsAPI.getCached (caching the altered version),
to filter the lists under latest_version.metadata.contents and (only in getCached) latest_version.docs_blob.contents
to remove any items with content_type module_utils or doc_fragments.

This also changes any previous code using latest_version.contents to use latest_version.metadata.contents instead.

Cc @newswangerd , @ZitaNemeckova

Affected screens:

• list of collections (counters)
• list of collections under namespace (counters)
• collection detail, documentation tab (left side list)
• collection detail, contents tab (counter and list)

Before:

After:

[himdel]

Updated to also fix the list screen counters, move the filtering to CollectionsApi, and deprecate latest_version.contents in favor of latest_version.metadata.contents :).

[patchback]

Backport to stable-4.3: 💔 cherry-picking failed — conflicts found

❌ Failed to cleanly apply c139cc7 on top of patchback/backports/stable-4.3/c139cc7839624be05a1d02a548ad2e6e6d318db3/pr-340

Backporting merged PR #340 into master

1. Ensure you have a local repo clone of your fork. Unless you cloned it
   from the upstream, this would be your origin remote.
2. Make sure you have an upstream repo added as a remote too. In these
   instructions you'll refer to it by the name upstream. If you don't
   have it, here's how you can add it:

   $ git add remote upstream https://github.com/ansible/ansible-hub-ui.git

3. Ensure you have the latest copy of upstream and prepare a branch
   that will hold the backported code:

   $ git fetch upstream
   $ git checkout -b patchback/backports/stable-4.3/c139cc7839624be05a1d02a548ad2e6e6d318db3/pr-340 upstream/stable-4.3

4. Now, cherry-pick PR CollectionDocs: filter out doc_fragments and module_utils #340 contents into that branch:

   $ git cherry-pick -x c139cc7839624be05a1d02a548ad2e6e6d318db3

   If it'll yell at you with something like fatal: Commit c139cc7839624be05a1d02a548ad2e6e6d318db3 is a merge but no -m option was given., add -m 1 as follows intead:

   $ git cherry-pick -m1 -x c139cc7839624be05a1d02a548ad2e6e6d318db3

5. At this point, you'll probably encounter some merge conflicts. You must
   resolve them in to preserve the patch from PR CollectionDocs: filter out doc_fragments and module_utils #340 as close to the
   original as possible.
6. Push this branch to your fork on GitHub:

   $ git push origin patchback/backports/stable-4.3/c139cc7839624be05a1d02a548ad2e6e6d318db3/pr-340

7. Create a PR, ensure that the CI is green. If it's not — update it so that
   the tests and any other checks pass. This is it!
   Now relax and wait for the maintainers to process your pull request
   when they have some cycles to do reviews. Don't worry — they'll tell you if
   any improvements are necessary when the time comes!

🤖 @patchback
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