Added Slack notification for verify and test

[Jay07GIT]

Changes:-

Added Slack notification for verify and test in github workflows.

[mdb]

Hi @Jay07GIT - Could you elaborate a bit on why you'd like to see terraform-provider-vinyldns GitHub Actions send Slack notifications? And what Slack instance do you intend to notify?

[Jay07GIT]

Hi @Jay07GIT - Could you elaborate a bit on why you'd like to see terraform-provider-vinyldns GitHub Actions send Slack notifications? And what Slack instance do you intend to notify?

Intention is to notify slack, when PR commit is passed/failed with tests in github.
Vinyldns-alerts is the slack channel which will be notify, when committed code is passed/failed.