[eCash dev libraries] [p8 ecash-ops] Add pushdata-bitcoin

Summary:
T2847

Depends on D12861

Bring pushdata-bitcoin into the monorepo. We need this to make sure all dependencies are on the same page.

Bitcoin state:

minimaldata requires bitcoin-ops and pushdata-bitcoin as a dependency
pushdata-bitcoin requires bitcoin-ops as a dependency

BCH state:

minimaldata requires bitcoincash-ops and pushdata-bitcoin as a dependencies
pushdata-bitcoin still using bitcoin-ops as a dependency

eCash desired end state:
We want all of these libraries to depend only on eCash versions. Hence,

ecash-minimaldata will require ecash-ops and pushdata-ecash
pushdata-ecash will require ecash-ops

These libraries have been static for a long time and this is expected to continue. However, we cannot expect new developers on eCash to understand the evolution of crypto forks and development for the last decade. So, it's important we keep eCash specific versions of these packages (especially if they depend on each other) in one place. The ABC monorepo is the best option.

Test Plan:
Confirm this diff was created by

cd web
git clone https://github.com/bitcoinjs/pushdata-bitcoin.git
cd pushdata-bitcoin
rm -rf .git

Reviewers: #bitcoin_abc, emack

Reviewed By: #bitcoin_abc, emack

Differential Revision: https://reviews.bitcoinabc.org/D12864