Merge #13058: [wallet] createwallet RPC - create new wallet at runtime

Summary:
f7e153e95 [wallets] [docs] Add release notes for createwallet RPC. (John Newbery)
32167e830 [wallet] [tests] Add tests for createwallet RPC. (John Newbery)
942131774 [wallet] [rpc] Add createwallet RPC (John Newbery)

Pull request description:

Adds a `createwallet` RPC to dynamically create a new wallet at runtime.

Includes tests and release notes.

Tree-SHA512: e0d89e3ae498234e9db5b827c56804cbab64f18a1875e2b5e676172c110278ea1b9e93a8a61b8dd80e2f2a691490bf229e923e4ccb284a1d3e420b8317815866

Backport of Core PR13058
https://github.com/bitcoin/bitcoin/pull/13058/

Test Plan:

make check
test_runner.py

Reviewers: deadalnix, Fabien, jasonbcox, O1 Bitcoin ABC, #bitcoin_abc, fpelliccioni

Reviewed By: deadalnix, O1 Bitcoin ABC, #bitcoin_abc

Subscribers: fpelliccioni

Differential Revision: https://reviews.bitcoinabc.org/D4220