Hotfix: Sanctions check via Balancer API

[timjrobinson]

Description

Re-add the sanctions check (removed in: #2028), performing it using a Lambda running on the Balancer API instead.

PR to add the Lambda API endpoint: balancer/balancer-api#22

Type of change

• Bug fix (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)
• Dependency changes
• Code refactor / cleanup
• Documentation or wording changes
• Other

How should this be tested?

Perform same tests as in #2017. Ensure that normal wallets connect fine and sanctioned wallets are blocked

Checklist:

• I have performed a self-review of my own code
• I have requested at least 2 reviews (If the PR is significant enough, use best judgement here)
• I have commented my code where relevant, particularly in hard-to-understand areas
• If package-lock.json has changes, it was intentional.
• The base of this PR is master if hotfix, develop if not

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