Added FreeAgent integration

[omnone]

Proposed changes

I have added the FreeAgent integration file and make the proper changes to integration/index.ts . It fixes #115 .

Types of changes

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• [x ] Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation Update (if none of the other choices apply)

Checklist

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• [x ] I have read the CONTRIBUTING guide
• Lint and unit tests pass locally with my changes
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)
• Any dependent changes have been merged and published in downstream modules

Further comments

If this is a relatively large or complex change, kick off the discussion by explaining why you chose the solution you did and what alternatives you considered, etc...

[Frenchcooc]

LGTM 🎉