feat: support --format in manifest fetch command

[qweeah]

What this PR does / why we need it:
This PR add --format flag to manifest fetch command to support field formatting for OCI manifests.

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Related to #638

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 88.65979% with 11 lines in your changes are missing coverage. Please review.

Project coverage is 84.46%. Comparing base (85fbdab) to head (4ec65f9).

Files	Patch %	Lines
...md/oras/internal/display/content/manifest_fetch.go	85.71%	1 Missing and 1 partial ⚠️
...rnal/display/metadata/descriptor/manifest_fetch.go	77.77%	1 Missing and 1 partial ⚠️
...s/internal/display/metadata/json/manifest_fetch.go	75.00%	1 Missing and 1 partial ⚠️
...ternal/display/metadata/template/manifest_fetch.go	77.77%	1 Missing and 1 partial ⚠️
cmd/oras/internal/display/utils/utils.go	77.77%	1 Missing and 1 partial ⚠️
cmd/oras/root/manifest/fetch.go	92.85%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1295      +/-   ##
==========================================
+ Coverage   84.04%   84.46%   +0.41%     
==========================================
  Files          90       97       +7     
  Lines        3467     3541      +74     
==========================================
+ Hits         2914     2991      +77     
+ Misses        331      327       -4     
- Partials      222      223       +1     

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[shizhMSFT]

LGTM