Converting IRIS Alert Source from Hardcoded to Dynamic Alert Field Variable

[bvirgilioamnh]

Description

Updated the IRIS Alert Source field to read from the alert fields instead of being hardcoded. The alert source field has a default value of the original hardcoded value 'ElastAlert2'. This is to provided additional flexibility when using ElastAlert across multiple solutions.

Checklist

• I have reviewed the contributing guidelines.
• I have included unit tests for my changes or additions.
• I have successfully run make test-docker with my changes.
• I have manually tested all relevant modes of the change in this PR.
• I have updated the documentation.
• I have updated the changelog.

Questions or Comments

[jertel]

This looks useful, thank you for submitting it. Will you please update the schema.yml file to include the new IRIS param?

[bvirgilioamnh]

This looks useful, thank you for submitting it. Will you please update the schema.yml file to include the new IRIS param?

@jertel you bet, done! Should probably update the contributing.md, I missed that this even existed.

[bvirgilioamnh]

Thank you :)