Allow passing in args for the SRPM build

[mfocko]

When running an SRPM build via GitHub Action, allow to specify arguments passed to the packit SRPM command, either by:

• wrapping packit srpm with a script that takes care of the parameters, or
• having an environment variable that will be passed to the container, such as $ARGS

[ssbarnea]

Be careful about arguments as github actions are very limited on how they can pass args and their types. Basically only strings are possible and you cannot have an empty default value. I was hit by these limitation with ansible-lint action.

Still, if you use a wrapper, you could get around these limitations.