Create notification on Product & Community Registries Check nightly run

[thepetk]

Which area/kind this issue is related to?

/area ci
/area alizer

Issue Description

The nightly run which checks the starter projects of all stacks inside product and community registry should have an alerting mechanism in order to notify people for the status of the job. As a result a notification should be added after every run, as a message to the appropriate team channel so people can monitor easier the results of this job.

Acceptance Criteria

• Every nightly run should send a message to team channel with the result of the task.
• The message should follow the following format:
  * Status: [{red light emoji} failure | {green light emoji} success]
  * Severity: [for failure - medium | for success low]
  * In case of failure mention @ app-devfile in order to take action.
  * Title: Product & Community Registries Check
  * Description: Mention Branch and Commit, add a short message and link to logs

[thepetk]

Currently blocked from #1248

[feloy]

Similar to #1061

[thepetk]

Blocked by #1026

[thepetk]

Removing blocked label as I don't think is relevant anymore

[thepetk]

Putting item back to "in review" cause I'm still looking for a proper way to test the related PR

[thepetk]

PR devfile/alizer#43 is now ready for review