Add two alias to "oras manifest fetch"

[FeynmanZhou]

What is the version of your ORAS CLI

v1.2.0

What would you like to be added?

oras manifest fetch supports viewing the metadata of a manifest. Literally, fetch might not be very straightforward for the view operation here. Suggest adding two alias oras manifest inspect and oras manifest show to oras manifest fetch for usability.

Why is this needed for ORAS?

Avoid misunderstanding of oras manifest fetch.

Are you willing to submit PRs to contribute to this feature?

• Yes, I am willing to implement it.