[FEATURE REQUEST] Add x509 runner module to use in x509_v2 execution module for remote signing

[SndR85]

Is your feature request related to a problem? Please describe.
I would like to be able to handle the Salt master to do the remote signing for signing certificates. Currently it's required to have a minion which is called via peer communication the x509_v2 module to handle the signing on it.

Describe the solution you'd like
I would be able to have and use a runner module on the Salt master which will do the signing of the remote certificate that is requested by the Salt minion. I would be able to set use_runner to a value of True in the x509.certificate_managed-state to allow the use of this runner. Also in the peer_run config on the Salt master should be set which minion may request to to the remote signing.

Describe alternatives you've considered
I have created a runner module which handle the signing. I have created a copy of the current x509_v2 execution module and modified it to let the module use the runner module on the master. However, this isn't future proof as I have to keep the module in sync with the upstream module of Salt, which is used by the x509_v2 state.

Additional context
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Please Note
If this feature request would be considered a substantial change or addition, this should go through a SEP process here https://github.com/saltstack/salt-enhancement-proposals, instead of a feature request.