Add a new --format tree-full flag for oras discover

[Wwwsylvia]

As per the ORAS diagnose experience proposal, we should add a new --format tree-full flag for oras discover to control the detailed metadata output, such as printing the annotations.

oras/docs/proposals/diagnose-experience.md

Lines 72 to 74 in 5280c67

	- Deprecate the `--verbose` flag and keep `--debug` flag to avoid ambiguity. It is reasonable to continue using `--debug` to enable the output of `DEBUG` level logs as it is in ORAS. Meanwhile, this change will make the diagnose experience much more straightforward and less breaking since only ORAS `pull/push/attach/discover` commands have verbose output.
	- Make the verbose output of commands `pull`, `push`, `attach` as the default (status) output. See examples at the bottom.
	- Make the verbose output of command `discover` as a formatted output, controlled by `--format tree-full`.

[Horiodino]

Hi, I’m interested in working on this. If no one else is currently assigned, would it be alright if I take it on?

[Wwwsylvia]

Hi @Horiodino , thank you for volunteering! Sure please feel free to create a PR and let us know if anything is unclear.

Just a note: In #1558 we deprecated the --verbose flag for other commands but oras discover. It's time to apply the same for oras discover as well when we add --format tree-full to it.