Merge #16383: rpcwallet: default include_watchonly to true for watchonly wallets

72eaab073b tests: functional watch-only wallet tests (William Casarin)
72ffbdc579 doc: add release note for include_watchonly default changes (William Casarin)
003a3c73c0 rpcwallet: document include_watchonly default for watchonly wallets (William Casarin)
a50d9e6c0b rpcwallet: default include_watchonly to true for watchonly wallets (William Casarin)

Pull request description:

  Right now it's a bit annoying to deal with watchonly wallets, many rpc commands have an `include_watchonly` argument that needs to be explicitly set.

  Wallets created with `createwallet` can have a `disable_private_keys` parameter, for those wallets we already know that they are watchonly, so there's no reason to have to explicitly ask for it for every command. Instead we check this wallet flag when the `include_watchonly` parameter isn't set.

ACKs for top commit:
  achow101:
    Code review ACK 72eaab073b
  Sjors:
    ACK 72eaab073b
  promag:
    ACK 72eaab073b, code review only, didn't look closely to the test.
  kallewoof:
    ACK 72eaab073b
  fanquake:
    ACK 72eaab073b - I've looked over the changes, they make sense to me. Compiled and ran the tests etc.

Tree-SHA512: d3646b55e97f386594d7efc994f0712f3888475c6a5dc7f131ac9f8c49bf5d4677182b88f42b34152abe1ad101ecadd152b4c20e9d3c1267190db36f77ab8bd7

test/functional/test_runner.py

@@ -129,6 +129,8 @@ BASE_SCRIPTS = [
     'wallet_multiwallet.py --usecli',
     'wallet_createwallet.py',
     'wallet_createwallet.py --usecli',
+    'wallet_watchonly.py',
+    'wallet_watchonly.py --usecli',
     'interface_http.py',
     'interface_rpc.py',
     'rpc_psbt.py',