[eCash dev libraries] [p3 ecash-ops] Change name of npm module in package.json

Summary:
T2847

Depends on D12856

Change name of to-be-published npm module to ecash-ops. Add a CHANGELOG.md to describe the change.

Test Plan: Confirm changes are only semantic

Reviewers: #bitcoin_abc, emack

Reviewed By: #bitcoin_abc, emack

Differential Revision: https://reviews.bitcoinabc.org/D12857