Add Custom Docker Build Push action to all Community Edition service repositories

[Exairnous]

The Custom Docker Build Push action enables easy, reproducible builds of Docker images that can be pushed to a container registry of your choice and should help make it easier to customize Community Edition instances, test pull requests/development branches, and provide Docker images of long running branches (large alpha/beta features) for community testing. As such, a workflow file for it should be added to each Community Edition service repository.

PR that can be used as a template: Hubs-Foundation/dialog#62

Repositories to update:

• certbotbot (repository not present yet)
  • PR:
• coturn (repository not present yet)
  • PR:
• dialog
  • PR: Add Custom Docker Build Push GitHub Workflow dialog#62
• hubs
  • PRs: Add GitHub workflow file to build/tag/push custom docker images hubs#6525 Force the repository name to be lowercase in the custom docker workflow hubs#6530
• nearspark
  • PR: Add Custom Docker Build Push GitHub Workflow nearspark#31
• pgbouncer
  • PR:
• photomnemonic
  • PR: Add Custom Docker Build Push GitHub Workflow photomnemonic#31
• reticulum
  • PR: Add GitHub workflow file to build/tag/push custom docker images reticulum#726
• speelycaptor
  • PR:
• spoke
  • PR: Add GitHub workflow file to build/tag/push custom docker images Spoke#1305

Note:

The original PR for this action was Hubs-Foundation/hubs#6525. Support for mixed case repositories was added in Hubs-Foundation/hubs#6530 (mixed case support was initially required for the Spoke repository and then included with the rest).