[Cashtab] Airdrop Option - minimum etoken holder balance eligibility
Summary: As per T2371, new option for airdrop organiser to restrict airdrop to users who hold a custom minimum amount of their eToken.
Test Plan:
- execute standard airdrop calculation to ensure no regression
- toggle the 'Minimum eToken holder balance' option and ensure the number input is rendered
- attempt to enter in a negative or non-numeric input and verify validation error
- specify a valid minimum etoken balance that will filter out a portion of the original recipient list. Ensure the pro rata airdrop amount is calculated correctly amongst the remaining recipients (i.e. the Total XEC Airdrop is split across the qualified recipients in full)
Reviewers: bytesofman, #bitcoin_abc
Reviewed By: bytesofman, #bitcoin_abc
Differential Revision: https://reviews.bitcoinabc.org/D11291