Add RemoveDocument API

[chacha912]

What this PR does / why we need it?

• Add RemoveDocument API
• Modify WatchDocument API

What are the relevant tickets?

Ref: yorkie-team/yorkie#484
Ref: yorkie-team/yorkie#491

Does this PR introduce a user-facing change?:

The new approach is to establish a stream connection for each document
instead of watching multiple documents on a single stream.
As a result, the issue of disconnecting and reconnecting the stream
when multiple documents are attached has been resolved.
Consequently, the client events that were tested have also been modified as shown below.
The event marked in red does not occur. - Refer to #484 for the previous test flow

Checklist

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

[codecov]

Codecov Report

Merging #480 (aa2d2cf) into main (7482aad) will increase coverage by 0.11%.
The diff coverage is 88.38%.

@@            Coverage Diff             @@
##             main     #480      +/-   ##
==========================================
+ Coverage   89.57%   89.68%   +0.11%     
==========================================
  Files          67       67              
  Lines        5410     5596     +186     
  Branches      528      542      +14     
==========================================
+ Hits         4846     5019     +173     
- Misses        381      386       +5     
- Partials      183      191       +8     

Impacted Files	Coverage Δ
src/core/client.ts	73.39% <71.17%> (-4.14%)	⬇️
test/integration/document_test.ts	98.98% <99.19%> (+0.34%)	⬆️
src/api/converter.ts	89.00% <100.00%> (+0.02%)	⬆️
src/document/change/change_pack.ts	100.00% <100.00%> (ø)
src/document/document.ts	81.98% <100.00%> (+2.98%)	⬆️
src/util/error.ts	100.00% <100.00%> (+50.00%)	⬆️
test/helper/helper.ts	74.07% <100.00%> (+3.24%)	⬆️
test/integration/client_test.ts	100.00% <100.00%> (ø)

... and 3 files with indirect coverage changes

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[hackerwins]

Thanks for your contribution.
Overall good. I left a few questions.