What this PR does / why we need it:
Introduces a new --format flag to the oras repo tags command, with 3 format options: text, json, and go-template.

Notes: This PR was implemented using GitHub Copilot with the Claude 3.7 model, with some manual adjustments. The prompt used was:

#codebase Enable --format json for oras repo tags command. Similar to oras discover --format json. You can define metadata handlers for the output. You need to take a closer look into the structure of cmd/oras/internal/display and understand the code structure of the existing commands.

Usage:
oras repo tags myregistry.com/myrepo --format json

{
"tags": ["foo", "bar"]
}

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Fixes part of #1547

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?