Feat/chains - Githubissues

Proposed changes

Adds support for polygon and fraxtal on the ledger connection.

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What types of changes does your code introduce to agents-aea? Put an x in the boxes that apply

[ ] Bugfix (non-breaking change which fixes an issue)
[x] New feature (non-breaking change which adds functionality)
[ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)

Put an x in the boxes that apply.

[x] I have read the CONTRIBUTING doc
[x] I am making a pull request against the develop branch (left side). Also you should start your branch off our develop.
[x] Lint and unit tests pass locally with my changes and CI passes too
[ ] I have added tests that prove my fix is effective or that my feature works
[ ] I have checked that code coverage does not decrease.
[ ] I have added necessary documentation (if appropriate)
[ ] Any dependent changes have been merged and published in downstream modules

N/A