[eCash dev libraries] [p9 ecash-ops] Change folder name from pushdata-bitcoin to pushdata-ecash

Summary:
T2847

Depends on D12864

Changing directory name as prep for changing npm package name, pushdata-bitcoin to pushdata-ecash

Test Plan: Confirm this is only a directory change. Confirm no typo in intended name.

Reviewers: #bitcoin_abc, emack

Reviewed By: #bitcoin_abc, emack

Differential Revision: https://reviews.bitcoinabc.org/D12865