Updated base buy currency from USD to ETH in buy token trade modal

[mzparacha]

Link to Issue

Closes: #10248

Description of Changes

Updated base buy currency from USD to ETH in buy token trade modal

"How We Fixed It"

N/A

Test Plan

1. Set FLAG_TOKENIZED_COMMUNITY=true in .env
2. Visit /communities and press "Launch Token" to create a token-based community
3. Visit that community and attempt to open the buy token trade modal from the community token widget "Buy" button
4. Verify that the buy amounts are in ETH
5. Verify that changing buy amount correctly gets reflects in the modal (in pricing conversions, receipt details and the "bought token" amount)
6. Verify that buy the token works correctly and you received the correct buy amounts as specified in the buy receipt.

Deployment Plan

N/A

Other Considerations

N/A