Webhooks for notifying Athens of a new module/version

[arschles]

Is your feature request related to a problem? Please describe.

It would be nice for module authors to tell an Athens instance when a new version of their module is published, without relying on someone to do a go get for that new version.

Describe the solution you'd like

A simple webhook that can be called which:

• Notifies Athens of a new module@version
• Prompts Athens to go fetch that module@version and store it in its storage
  • Just as if someone ran a go get against Athens

Describe alternatives you've considered

None

Additional context

I'm reviving this idea from the following related issues:

• https://github.com/gomods/athens/issues/106
• https://github.com/gomods/athens/issues/10
• https://github.com/gomods/athens/issues/104

cc/ @marpio

[phaizel]

I am keen to work on this.

[arschles]

@phaizel great! DM me if you like and I'll help get you started

[arschles]

@phaizel are you still interested in doing this one?

[arschles]

Please see #1341 for a more detailed idea of how this could be implemented