Implement a default user_agent string

[lleyton]

This implements a default user_agent string as described in https://github.com/rpm-software-management/dnf5/blob/main/doc/dnf5.conf.5.rst.

I also moved the OSRelease class from the COPR plugin into a library util for reuse, as well as a few other functions in conf/vars.

[packit-as-a-service]

We were not able to find or create Copr project packit/rpm-software-management-dnf5-1590 specified in the config with the following error:

Packit received HTTP 500 Internal Server Error from Copr Service. Check the Copr status page: https://copr.fedorainfracloud.org/status/stats/, or ask for help in Fedora Build System matrix channel https://matrix.to/#/#buildsys:fedoraproject.org.

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Unless the HTTP status code above is >= 500, please check your configuration for:

1. typos in owner and project name (groups need to be prefixed with @)
2. whether the project name doesn't contain not allowed characters (only letters, digits, underscores, dashes and dots must be used)
3. whether the project itself exists (Packit creates projects only in its own namespace)
4. whether Packit is allowed to build in your Copr project
5. whether your Copr project/group is not private

[kontura]

This is great, thank you!

I have added just one note + can you fix the formatting issues detected by the Pre Commit Hooks? You can see the specific issues here in the Details.

[kontura]

While working on some related functionality I noticed couple more issue.

[kontura]

@lleyton any update here?

We require these changes also for rpm-software-management/ci-dnf-stack#1501.

[lleyton]

oh sorry! missed your replies, gonna push changes to address the issues in a bit

[lleyton]

Should be good now!

[kontura]

Great, thanks.

There is still couple formatting issues.
You can use the pre-commit to do the formatting automatically with pre-commit run --all-files.

[kontura]

The failing CI for 41 and rawhide is not related.

[lleyton]

formatting issues should be fixed