Add deploy start & success notifications & multiple slack channel support

[mike-sheppard]

Summary

• Add deploy start notification Add option to send a pre-deploy message #3
• Update readme with info for newer versions of Trellis + variable name updates
• Add git username Use the commit author in messages #4
• Add a link to the deployed site env. URL
• Add a link to the deployed commit on GitHub for quick lookup (if using GitHub, otherwise show git sha as before)
• Simplify message into a single line for quick scanning (after a couple deploys the longform messages cause quite a bit of scrolling)
• Ignore errors, so deployments do not fail Ignore error to make deploy passes #8
• Multiple Slack channels/organisations support - Notify Multiple Slack Webhooks #9

Preview

[tangrufus]

Awesome idea!

[dalepgrant]

@tangrufus I've updated this a little further as Slack now doesn't allow one webhook to post to multiple channels, at least when creating a new App. My changes allow a channel to be notified per site, per environment, as well as notifying multiple channels per deploy (Mike's change). I've also moved the slack deploy token to vault. There's a PR up for @mike-sheppard here (#3) - I figured it was best to merge into his changes first but I can PR direct if that's easier.

Feedback welcome from all 👍

[codepuncher]

@dalepgrant I'd definitely prefer merging the work from you and @mike-sheppard in one to simplify tagging the next release - so hopefully we can move forward with that.

[dalepgrant]

@codepuncher happy to help, let me know if you need anything more from me.

Same to you @mike-sheppard 👍

[codepuncher]

@dalepgrant I can see that you've submitted a PR here, so I guess we'll just wait to hear back from @mike-sheppard

[mike-sheppard]

Sure thing, that should be sorted now 👍🏻

[codepuncher]

Cheers, @mike-sheppard. I'll try and get this tested this week. Thanks again for the PR!

[mike-sheppard]

Hey @codepuncher any issues during testing? Let me know if I can do anything to get this merged in.

Nice one!
Mike