[backport#15713] Add BroadcastTransaction utility usage in Chain interface

Summary:
Access through a broadcastTransaction method.
Add a wait_callback flag to turn off race protection when wallet
already track its tx being in mempool

Standardise highfee, absurdfee variable name to max_tx_fee

We drop the P2P check in BroadcastTransaction as g_connman is only
called by RPCs and the wallet scheduler, both of which are initialized
after g_connman is assigned and stopped before g_connman is reset.

https://github.com/bitcoin/bitcoin/pull/15713/commits/8c8aa19b4b4fa56cd359092ef099bcfc7b26c334

Depends on D6272

Partial backport of Core PR15713

Test Plan:

ninja check-all

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D6273