Fixes #37504 - send 404 to v2 client requesting v1/search

[ianballou]

What are the changes introduced in this pull request?

Podman no longer has libpod in the HTTP_USER_AGENT header. Now, we should check for v2 clients instead. This should apply to docker as well.

Considerations taken when implementing this change?

/_catalog and /v1/search are both removed from the OCI spec, but we should keep supporting them for now since the clients allow it.

What are the testing steps for this pull request?

1. Test podman search with unauthenticated pull off (default) and some search text:

$ podman search `hostname`/ubuntu

NAME                                                                                                                     DESCRIPTION
centos9-katello-devel.manicotto.example.com/default_organization-buttermilk_biscuits-docker_ubuntu                       
centos9-katello-devel.manicotto.example.com/default_organization-library-export_view-buttermilk_biscuits-docker_ubuntu   
centos9-katello-devel.manicotto.example.com/default_organization-buttermilk_biscuits-ubuntu                              
centos9-katello-devel.manicotto.example.com/default_organization-library-container_push_view-buttermilk_biscuits-ubuntu 

2. Try the code as well with a Docker client, just to be safe. Installed Docker-CE via their online instructions.

[sjha4]

Before PR: 200 status code

After PR: 404 returned.

Code makes sense after reading description. Ack 👍🏼