Move features docs to its own file

[kmcginnes]

Description

• Moves feature descriptions to its own file: /additionaldocs/features/README.md
• Update link to roadmap
• Add smaller section in root readme that links to new features readme file
• No content changes to moved content other than title, roadmap link, and heading level

Validation

• Check content in new section
• Check links still work

Related Issues

• Part of Add documentation for Gremlin query editor #846

Check List

• I confirm that my contribution is made under the terms of the Apache 2.0
  license.
• I have run pnpm checks to ensure code compiles and meets standards.
• I have run pnpm test to check if all tests are passing.
• I have covered new added functionality with unit tests if necessary.
• I have added an entry in the Changelog.md.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 33.24%. Comparing base (a899239) to head (955987e).
Report is 20 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #957      +/-   ##
==========================================
+ Coverage   30.72%   33.24%   +2.52%     
==========================================
  Files         525      523       -2     
  Lines       23627    21287    -2340     
  Branches     1408     1507      +99     
==========================================
- Hits         7259     7077     -182     
+ Misses      16241    14093    -2148     
+ Partials      127      117      -10     

Flag	Coverage Δ
unittests	33.24% <ø> (+2.52%)	⬆️

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