DNF5 plugin is missing the search command

[FrostyX]

The DNF4 feature looked like this:

$ dnf-3 copr search gleam
======================================================================================================= Matched: gleam =======================================================================================================
frostyx/gleam : Gleam is a general-purpose, concurrent, functional high-level programming
              : language that compiles to Erlang or JavaScript source code. Gleam is
              : a statically-typed language, which is different from the most popular languages
              : that run on Erlang’s virtual machine BEAM, Erlang and Elixir.
@copr/PyPI : This repository contains packages from Python Package Index (PyPI) generated by the automatic tool - pyp2spec.
           : Their quality may vary, use at your own risk.
           :
tmelo/PyPI2 : All packages from PyPI built as RPM packages with only python2 subpackage.
@rubygems/rubygems : Automatic rebuilds of gems from rubygems.org as RPM packages.
                   :
                   : Packages have have been created by [gem2rpm](https://github.com/fedora-ruby/gem2rpm) tool. The results may or not work. Try it your selves.
@copr/PyPI3 : All packages from PyPI built as RPM packages with only python3 subpackage.

Copr web interface now supports searching by project name, owner name, and package name, so we could have optional parameters for this.

I think it's fine if we decide not to implement this in C++ in the DNF5 plugin but rather implementing #2646. We don't need both.