Implemented route /v2/_catalog API functionality

[keyskull]

No description provided.

[gabivlj]

Thank you for your contribution!

[keyskull]

Anything else that I need to cover to merge this PR to the branch?

[skepticfx]

It looks there is no more user namespace or special authentication involved here. Shouldn't catalog be restricted to a privileged user?

[gabivlj]

Anything else that I need to cover to merge this PR to the branch?

Sorry forgot to submit my review :-). There are some comments I wanted to be addressed

[keyskull]

About @skepticfx mentioned authentication feature, @gabivlj do you know we should have restrictions for each user or just general authentication?

[gabivlj]

Thank you @keyskull, I had another nit but once that is addressed I think all is ok to merge from my side.

[gabivlj]

About @skepticfx mentioned authentication feature, @gabivlj do you know we should have restrictions for each user or just general authentication?

We have some kind of read/write permissions. IMO this is already handled on the middleware side. What do you think @skepticfx?

[skepticfx]

@gabivlj registries don't allow access to this by default AFAIK. But I believe, this specific authorization check is not really relevant to this PR. Believe a middleware which does the right RBAC should handle this correctly. None of our middleware examples allow this today, but something to be cautious about.