Resolve "Make monitor more generic"

What does this MR do and why?

feat(template.Monitor): Display Monitor integration (#110 (closed))

fix(integration.Datadog): Fix not updated monitors when more than 50 defined

change(*.Monitor): Make monitors more generic

database_migration(Monitor): All monitor having an external_link containing a Datadog monitor URL (/.*datadoghq.*/) will be updated :

• external_reference will be populated from the monitor ID contained in the external_link
• integration will be populated with the value datadog

MR acceptance checklist

• My code follows the style guidelines of this project
• I ran pylint and other linters for modified files
• I have performed a self-review of my own code and tested it
• I have commented my code, particularly in hard-to-understand areas
• My changes generate no new warnings
• My code needed automated testing. I have added them (this is optional task)
• I have added user readable comment in the CHANGELOG

Closes #110 (closed)