Add C# Dev Kit extension

[ArinGhazarian]

This PR adds C# Dev Kit to the extensions list. It will install the C# extension and has a built in test explorer.

• [x] Did you write/update appropriate tests
• [x] Release notes updated (if appropriate)
• [x] Appropriate logging output
• [x] Issue linked
• [x] Docs updated (or issue created)
• [x] New package licenses are added to ThirdPartyNotices.txt (if applicable)

[github-actions[bot]]

Unit Test Results

810 tests   810 :white_check_mark:  22s :stopwatch:   1 suites    0 :zzz:   1 files      0 :x:

Results for commit e4aafffa.

:recycle: This comment has been updated with latest results.

[github-actions[bot]]

Package	Line Rate	Branch Rate	Complexity	Health
gei	79%	70%	519	✔
Octoshift	87%	76%	1272	✔
ado2gh	84%	78%	627	✔
bbs2gh	78%	73%	651	✔
Summary	83% (6821 / 8172)	75% (1534 / 2044)	3069	✔