[WIP] Reorganize docs

[neverett]

Why are the changes needed?

Reorganize documentation to make it easier for Flyte users to find and use information and for community members to contribute to documentation.

What changes were proposed in this pull request?

• Add new top-level categories
• Move docs pages into new categories as needed
• Consolidate duplicate information on different docs pages

Check all the applicable boxes

• [ ] I updated the documentation accordingly.
• [ ] All new and existing tests passed.
• [ ] All commits are signed-off.

Docs link

TK

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 60.19%. Comparing base (40dccab) to head (996ed39). Report is 387 commits behind head on master.

:exclamation: Current head 996ed39 differs from pull request most recent head 07c5c21. Consider uploading reports for the commit 07c5c21 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5286      +/-   ##
==========================================
+ Coverage   59.68%   60.19%   +0.50%     
==========================================
  Files         568      646      +78     
  Lines       41729    45654    +3925     
==========================================
+ Hits        24906    27481    +2575     
- Misses      14410    15581    +1171     
- Partials     2413     2592     +179     

Flag	Coverage Δ
unittests-datacatalog	69.31% <ø> (ø)
unittests-flyteadmin	58.78% <ø> (-0.05%)	:arrow_down:
unittests-flytecopilot	17.79% <ø> (ø)
unittests-flyteidl	79.30% <ø> (ø)
unittests-flyteplugins	61.94% <ø> (ø)
unittests-flytepropeller	57.32% <ø> (ø)
unittests-flytestdlib	65.75% <ø> (?)

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