feat: Add support for Micropub

[chocolate-pie]

What

Micropub (IndieWeb Living Standard 25 July 2020)のサポートを追加

Why

Closes #9523

Additional info (optional)

Checklist

• Read the contribution guide
• Test working in a local environment
• (If needed) Add story of storybook
• (If needed) Update CHANGELOG.md
• (If possible) Add tests

[codecov]

Codecov Report

Attention: Patch coverage is 17.80455% with 614 lines in your changes are missing coverage. Please review.

Project coverage is 64.36%. Comparing base (f8261a1) to head (c75569d).
Report is 438 commits behind head on develop.

Files	Patch %	Lines
...ckend/src/server/micropub/MicropubServerService.ts	16.07%	590 Missing ⚠️
packages/backend/src/server/FileServerService.ts	0.00%	21 Missing ⚠️
packages/backend/src/server/ServerService.ts	33.33%	2 Missing ⚠️
...ages/backend/src/server/web/ClientServerService.ts	0.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##           develop   #13144       +/-   ##
============================================
- Coverage    79.95%   64.36%   -15.59%     
============================================
  Files          956      987       +31     
  Lines       108864   111504     +2640     
  Branches      8413     4369     -4044     
============================================
- Hits         87045    71775    -15270     
- Misses       21819    39697    +17878     
- Partials         0       32       +32     

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[github-actions]

このPRによるapi.jsonの差分

差分はこちら

Get diff files from Workflow Page

[tamaina]

本体のコード一言一句見てないけどテスト動いてるしApprove

[syuilo]

Micropubが何なのかよく分かってないわね

[chocolate-pie]

簡単に言うとノートの投稿をソフトウェアが個別で提供しているAPIを意識せずにより簡単にできるようにした仕様で、
拡張機能などでMisskeyに限らずデータの共有とかは簡単にできるようになります。しかしMicropubは今のところ特に著名なソフトウェアが実装しているわけでもありませんしActivityPub C2S APIもPleromaで久しくメンテナンスされていないようなので別に実装しなくてもいいのかもしれません。