Add remove document command to CLI

[emplam27]

What this PR does / why we need it:

Add RemoveDocumentAdmin API in Admin client & CLI command

• dashboard can use gRPC API for remove document
• User can use CLI command for remove document

Which issue(s) this PR fixes:

Fixes #464

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

$ yorkie document remove {project name} {document key}

Additional documentation:

Checklist:

• Added relevant tests or not required
• Didn't break anything

[codecov]

Codecov Report

Merging #540 (9dd9211) into main (ff4d8cc) will decrease coverage by 0.60%.
The diff coverage is 0.00%.

❗ Current head 9dd9211 differs from pull request most recent head a531ed1. Consider uploading reports for the commit a531ed1 to get more accurate results

@@            Coverage Diff             @@
##             main     #540      +/-   ##
==========================================
- Coverage   50.92%   50.32%   -0.60%     
==========================================
  Files          65       65              
  Lines        5978     6057      +79     
==========================================
+ Hits         3044     3048       +4     
- Misses       2539     2614      +75     
  Partials      395      395              

Impacted Files	Coverage Δ
server/backend/database/memory/database.go	51.13% <0.00%> (-1.44%)	⬇️
server/backend/database/mongo/client.go	24.11% <0.00%> (-0.80%)	⬇️
server/backend/database/mongo/indexes.go	50.00% <ø> (ø)
server/rpc/admin_server.go	53.78% <0.00%> (-8.36%)	⬇️

... and 2 files with indirect coverage changes

[hackerwins]

Thanks for your contribution.
We can remove documents with CLI.