Add config option

[djanickova]

Hey, I just made a Pull Request!

Added another part to the config so that the PR creation can be enabled/disabled.
By default, the text of the notification differs when the user has PR creation disabled (previous default message) and enabled (new default message). They can still configure a custom message as well and there is another variable supported for it ($PR_LINK). If the PR creation fails, the notification is still sent with a default text (together with the error details and a link to the docs).

I also updated the README and create a new .md file dedicated just for this feature, which I is linked from the main README and can also be found in the notification of a failed PR and the created PR description.

This is an example screenshot of when 2 PRs were created (for both Github and Gitlab) and I provided a custom title and description for the notification:

The config in this case was:

scaffolder:
  notifications:
    templateUpdate:
      enabled: true
      message:
        title: 'Custom title for $ENTITY_DISPLAY_NAME'
        description: 'The template used to create $ENTITY_DISPLAY_NAME has been updated to a new version. PR link: $PR_LINK'
  pullRequests:
    templateUpdate:
      enabled: true

This is an example screenshot of when 2PRs were not created because of an error, so the default message together with the error details and link to documentation was sent in the description:

I will be happy to hear any feedback!

✔️ Checklist

• A changeset describing the change and affected packages. (more info)
• Added or updated documentation
• Tests for new functionality and regression tests for bug fixes
• Screenshots attached (for UI changes)
• All your commits have a Signed-off-by line in the message. (more info)

[dzemanov]

Thank you, works great!

Tested these cases:

• No notifications or prs enabled
• Only notifications are enabled
• Only prs are enabled + only prs are enabled with custom message and title
• both notifications and prs are enabled - default messages and custom messages
• tested errors