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:

• [x] 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[bot]]

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 :warning:
...rnal/display/metadata/descriptor/manifest_fetch.go	77.77%	1 Missing and 1 partial :warning:
...s/internal/display/metadata/json/manifest_fetch.go	75.00%	1 Missing and 1 partial :warning:
...ternal/display/metadata/template/manifest_fetch.go	77.77%	1 Missing and 1 partial :warning:
cmd/oras/internal/display/utils/utils.go	77.77%	1 Missing and 1 partial :warning:
cmd/oras/root/manifest/fetch.go	92.85%	0 Missing and 1 partial :warning:

Additional details and impacted files

```diff @@ 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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