Create RPM packaging for slim

[Rohansjamadagni]

What

Add support for building source and binary rpms

Why

I saw it on the roadmap and thought I'd contribute. Should be useful for a lot of folks running on RHEL based distros.

How Tested

Tested on fedora and almalinux containers.
Steps followed for testing:

dnf install -y git golang rpmdevtools
cd && git clone https://github.com/Rohansjamadagni/slim && cd slim
spectool -g -R packaging/slim.spec
rpmbuild -ba  packaging/slim.spec
dnf install -y /root/rpmbuild/RPMS/x86_64/slim-1.40.6-1.el9.x86_64.rpm
slim --version

I could probably add a GitHub action to automatically build the rpm and publish the artifacts. Please let me know if this would be helpful or if you have any other questions.

[kcq]

thank you @Rohansjamadagni ! reviewing the PR