Add support for enabling OpenRC service on a specific runlevel

[sengo4hd]

• Pull request is based on the default branch (3.x at this time)
• Pull request includes tests for any new/updated operations/facts
• Pull request includes documentation for any new/updated operations/facts
• Tests pass (see scripts/dev-test.sh)
• Type checking & code style passes (see scripts/dev-lint.sh)

Hello and thank you for your work on this project :)
I find the design to be very clear and well-thought, making it easy to engage with contributing.

I want to use pyinfra to enable a nftables service on the boot runlevel with OpenRC. I noticed that the openrc.service operation would always trigger a change on every run even though the service was never really enabled on this runlevel. This is because the change was always happening on the default runlevel, ignoring the configuration.

I would like to propose these changes:

• A noop message for when a service is already enabled/disabled to help with troubleshooting.
• Support for enabled/disabling services on a specific runlevel, as expected from the documentation.

I did not find it necessary to update the openrc.service documentation.
I also fixed a small typo in a link in the contributing documentation.