Add search builtin

This allows searching for applications easily greatly improving
the UX of the cli. This relies upon appstream data which currently
must be updated with `flatpak update --appstream`.

Closes: #1136
Approved by: mwleeds
This commit is contained in:
Internal Server Error - Gitea: Git with a cup of tea
500 Internal Server Error

Gitea Version: 1.28.0+dev-477-g8b6ad49a5f