[Cashtab][Alias] Implement getAliasesForAddress

Summary:
T3216

Add the new getAliasesForAddress function in aliasUtils.js to wrap around the fetch call to alias-server's address endpoint.

Test Plan: npm test

Reviewers: bytesofman, #bitcoin_abc

Reviewed By: bytesofman, #bitcoin_abc

Differential Revision: https://reviews.bitcoinabc.org/D14189