Restructure docs folder and website for usability and clarity

[dtzhou2]

What this PR does and why is it needed

1. Clean up old/unused files in docs/installation
2. Add in files that werent referenced by mkdocs but considered relevant documentation
3. Delete unused and irrelevant documentation (running_rpm.md)
4. Move items in the website around for clarity (Introduction/introduction served the same purpose as getting started/introduction so I combined those sections and moved launching-ovn-kube-on-kind into the getting started folder since it seemed more relevant there)

Which issue(s) this PR fixes

Fixes #

Special notes for reviewers

Changed index.md to README.md. Tested with mkdocs and apparently using index.md instead of README.md means it will not properly be in a subheading in the website columns. Using README.md is workaround for that problem

How to verify it

Details to documentation updates

Instead of changing documentation mostly making sure documentation more accessible.

Description for the changelog

Refactored docs folder structure

Does this PR introduce a user-facing change?

[coveralls]

coverage: 52.728% (+0.03%) from 52.702%
when pulling 8c571d0 on dtzhou2:doc_rearrangement
into bf06da7 on ovn-org:master.

[tssurya]

hold this change, its conflicting with https://github.com/ovn-org/ovn-kubernetes/pull/4333/files#diff-98d0f806abc9af24e6a7c545d3d77e8f9ad57643e27211d7a7b896113e420ed2 why is the index.md file getting removed like that? IMHO its better to remove the introduction bit from getting started..

[dtzhou2]

I renamed index.md to README.md so we could both include it in the nav bar and use it as the homepage

[tssurya]

Overview should be first, not sure why Getting started is moving positions here

[dtzhou2]

I had getting started in the first position because it contained the index/homepage for the project since I deleted the introduction subheading.

[tssurya]

I see, I don't think we need overview in getting started so we can keep things where they are in that case at least that's the change I had proposed in my PR for the release cut, but ofc I don't have strong opinions either ways.

[dtzhou2]

I felt that it was better for UI simplification since right now the index page gets its own subheading, which seems a little wasteful. Maybe instead we can just remove the subheading and keep everything else where it is?

[tssurya]

yeah that's the bit I did in my PR PTAL, if you rebase this we can have another round of reviews
the other thing I was thinking is.. is there any use to keep the deprecated docs at all? (thinking out loud here.. will ask team for second opinion on if we should probably just get rid of these ...)

[github-actions]

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