Split prow config from prow codebase

[stevekuznetsov]

We're getting close to being ready for the move. Items we know we need to accomplish is here:

• reconfigure config updater for prow.k8s.io Allow config-updater plugin to look for Prow config under config/ #11781
• move remaining config files to config/ and run the config-bootstrapper in case any changed had landed in between [WIP] Move configuration files to their new home #11784
• ensure all references to original config locations are updated
• move prow/cluster to config/cluster
• ensure all auto-bump etc automation around prow/cluster is updated
• submit KEP to create repo

/cc @spiffxp @fejta @cjwagner @BenTheElder @krzyzacy

[stevekuznetsov]

/assign

[fejta-bot]

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/lifecycle stale

[StevenACoffman]

/remove-lifecycle stale

[spiffxp]

Need to see what PR's modify config.yaml and plugin.yaml and decide if we want those to go through rebase fun

[spiffxp]

/milestone v1.16
/assign

[spiffxp]

/assign @cjwagner