Add integration test to verify that fundMax uses the protocol-level
maximum channel size instead of the user-configured maxChanSize. The
test uses a table-driven approach to cover both non-wumbo and wumbo
scenarios, creating nodes with restrictive maxChanSize (5M sats) and
verifying that fundMax still creates channels at the protocol maximum.
The maxChanSize config option is documented to only apply to incoming
channel requests. However, when using fundMax with OpenChannel, the code
was incorrectly using maxChanSize as the upper bound for the outgoing
channel size.
This commit fixes the issue by using the protocol-level maximum
(MaxBtcFundingAmount or MaxBtcFundingAmountWumbo depending on wumbo
support) as the upper bound for fundMax operations.
Fixes#10468.
Yash Bhutwala