bld2repo and a corresponding mock config?

[praiskup]

Could we somewhat cooperate on creating an appropriate mock configuration
for the created local repository? This is just a rough idea/brainstorm,
"this" can be implemented in Mock directly, or anywhere else.

Currently, I tried to call bld2repo (with Red hat internal Koji server)
and then edited an existing (EL8) mock configuration and I'm getting
various errors (not being able to reproduce the build eventually).

Currently I'm getting:

...
No available modular metadata for modular package 'xmvn-subst-....module+....', it cannot be installed on the system
No available modular metadata for modular package 'xz-java-...module+.....', it cannot be installed on the system
Error: No available modular metadata for modular package
``