refactor: add handlers to manifest push commmand

[wangxiaoxuan273]

What this PR does / why we need it:

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Part of #1542

Please check the following list:

• Does the affected code have corresponding tests, e.g. unit test, E2E test?
• Does this change require a documentation update?
• Does this introduce breaking changes that would require an announcement or bumping the major version?
• Do all new files have an appropriate license header?

[codecov]

Codecov Report

Attention: Patch coverage is 85.00000% with 6 lines in your changes missing coverage. Please review.

Project coverage is 84.06%. Comparing base (ae989e8) to head (4cba0a4).

Files with missing lines	Patch %	Lines
cmd/oras/root/manifest/push.go	40.00%	3 Missing and 3 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1555      +/-   ##
==========================================
- Coverage   84.07%   84.06%   -0.02%     
==========================================
  Files         119      119              
  Lines        5325     5353      +28     
==========================================
+ Hits         4477     4500      +23     
- Misses        602      606       +4     
- Partials      246      247       +1     

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[qweeah]

@wangxiaoxuan273 Can you help resolve the conflict?

[qweeah]

This should belong to the metadata handler

[wangxiaoxuan273]

As discussed when doing oras manifest index create handlers, this function should be in status handler, as its output is like Pushed [registry] test.registry.io/test:v1. See this comment: #1509 (comment)

However, we may also need OnManifestPushed in metadata handler to output necessary metadata information. Future discussion may be needed.

In oras attach and oras push commands, this function is currently in metadata handler. We may need to move them to status handler in a future work item. cc: @shizhMSFT

[wangxiaoxuan273]

We need to discuss more on the effect of tty handlers.

[wangxiaoxuan273]

Ideal handler workflows:

1. Start operation (status)
2. Process nodes / tasks (status, metadata); Note: For each node, we have status and metadata
   a. Start Processing (status)
   b. Complete processing (status, metadata)
3. Complete operation (status, metadata)

[shizhMSFT]

Per offline discussion, we don't implement status update for "3. complete operation". Thus, we will drop OnManifestPushed. We will still keep OnManifestUploaded as the completion of the sub-task/sub-process. For naming convension, it is suggested to rename OnManifestUploaded to OnManifestPushed.

[shizhMSFT]

For metadata, we need OnManifestPushed (or equivalent) for the record of sub-task/sub-process and OnComplete for the record of completion of operation (mainly for rendering if the output format does not support streaming. e.g. JSON).

[shizhMSFT]

Please follow @qweeah's comments

[qweeah]

Suggested change

	func (h *ManifestPushHandler) OnCompleted(desc ocispec.Descriptor) error {
	func (h *ManifestPushHandler) OnCompleted() error {

[wangxiaoxuan273]

According to offline discussion, OnCompleted should have no parameters. Created #1573