Docs: Fix rst leftover errors

[pedro-psb]

After migrating the docs to markdown, there is still some fair amount of documents with rst leftover errors.

Some common pattern observed:

• admonitions blocks without indentation
• a lot of backticked words (`some-word`) were internal links before. That's a bit hard to distinguish now and is the least automatable IHO.
• stuff with :something:, which I think are different kinds of links

  grep -rE ':[a-z]+:' staging_docs/

• stuff with {something}. Mostly {class}, which reference generated code API doc:

  grep -rE '\{[a-z_\-]+\}`' staging_docs/

[AndersBennedsgaard]

I don't know if it is relevant here, since I'm a newcomer for Pulp, but there are also a lot of broken links, and links to incorrect places. A couple of examples:

• Pulp-python Overview references the REST API for the pulp_python in https://pulpproject.org/pulp_python/docs/user/guides/00-overview/restapi.html, which doesn't exist.
• The Backup section in Pulp operator Configure and Run Backup/Restore references the PulpBackup CR, which doesn't exist, so it redirects to the table of contents

You hit many other examples if you just browse through the website. It might make sense to have some automation for detecting broken links. We use tcort/markdown-link-check successfully as validation in a CI pipeline

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Another note: the documentation needs some sort of sorting/weighting between pages. It doesn't make sense that the Pulp CLI how-to guides go "Configure (advanced) -> Configure (basic) -> Install":

[lubosmj]

This site is also completely broken: https://pulpproject.org/pulpcore/docs/dev/guides/plugin-walkthrough/.