Allow specifying a topic when subscribing to a document

[chacha912]

What this PR does / why we need it?

1. Subscribe to Document with Specified Target

In the case where there are multiple data (such as root.todos, root.counter, etc.)
in one document root, as in the example above, if you want to perform a specific task
only when root.todos is changed,

• as-is) you have to traverse the changeInfo.paths in the event value
  and check if the path($.todos) has been changed.
• to-be) You can specify the target path as $.todos
  and register a callback function to execute when the specified path is changed.
  So, in the example, the doc event occurs every time the document is changed,
  but the events for todos, counter, and quill are only triggered
  when their respective path or any of their nested values are changed.

// as-is
doc.subscribe((event) => {
  for (const changeInfo of event.value) {
    for (const path of changeInfo.paths) { 
      switch (path) {
        case path.startsWith('$.target'):
	   const key = path.split('.')[1];  // extract the key
           const target = doc.getRoot()[key];  
           // Do something...
           break;
      }
    }
  }
});

// to-be
doc.subscribe((event) => {
  // The callback will be called when the document is changed.(as before)
  // Do something...
});
doc.subscribe('$.target', (event) => { 
  // The callback will be called when the targetPath or any of its nested values change.
  const target = doc.getValueByPath('$.target') // you can get the value by path 
  // Do something...
});

2. Improvement of Event Value for Local/Remote Change

In document subscription, the event value provides an array of operations, which is difficult to use.
Provide useful information to the user from the operation.

• as-is)
  • IncreaseOperation { parentCreatedAt: TimeTicket, executedAt: TimeTicket, value: Primitive }
• to-be)
  • { type: 'increase', value: 1, path: '$.counter' }

doc.subscribe('$.target', (event) => { 
  // If the event.type is `local-change` or `remote-change`
  for (const changeInfo of event.value) {
    const {message, operations} = changeInfo;
    for (const op of operations) { 
      // ex) { type: 'increase', value: 1, path: '$.counter' }
      switch (op.type) {
        case 'increase':  
           // Do something...
           break;
      }
    }
  }
});

Any background context you want to provide?

What are the relevant tickets?

Fixes #445

Checklist

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

[codecov]

Codecov Report

Merging #487 (2147252) into main (0afacc0) will increase coverage by 0.47%.
The diff coverage is 88.66%.

@@            Coverage Diff             @@
##             main     #487      +/-   ##
==========================================
+ Coverage   89.71%   90.19%   +0.47%     
==========================================
  Files          69       69              
  Lines        5690     5985     +295     
  Branches      551      568      +17     
==========================================
+ Hits         5105     5398     +293     
+ Misses        390      381       -9     
- Partials      195      206      +11     

Impacted Files	Coverage Δ
src/document/json/array.ts	87.75% <ø> (ø)
src/document/operation/operation.ts	100.00% <ø> (ø)
test/helper/helper.ts	82.22% <ø> (+8.14%)	⬆️
test/integration/object_test.ts	100.00% <ø> (ø)
src/document/operation/select_operation.ts	50.00% <42.85%> (+11.11%)	⬆️
src/document/operation/style_operation.ts	54.16% <50.00%> (+4.16%)	⬆️
src/document/operation/increase_operation.ts	66.66% <57.14%> (+2.38%)	⬆️
src/document/operation/add_operation.ts	72.22% <62.50%> (+1.63%)	⬆️
src/document/operation/move_operation.ts	66.66% <62.50%> (ø)
src/document/operation/set_operation.ts	66.66% <62.50%> (-3.93%)	⬇️
... and 10 more

... and 3 files with indirect coverage changes

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[hackerwins]

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

[hackerwins]

LGTM.