Add airnode-deployer `fetch-files` command

[amarthadan]

Close #1159

[github-actions[bot]]

Visit the preview URL for this PR (updated for commit 39ba02b):

https://api3-docs--pr1161-deployer-fetch-files-apcf5tm2.web.app

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[dcroote]

Thanks - will test & review tonight

[wkande]

Deployed