Fallback function could be made payable.

[MicahZoltu]

https://github.com/safe-global/safe-contracts/blob/bf943f80fec5ac647159d26161446ac5d716a294/contracts/base/FallbackManager.sol#L61

One can use the FallbackManager to add functions to the safe, but since the fallback method it defines is not payable, one cannot use it to add any new payable functions. There is already a native receive handler, so value with empty data is allowed, but not a novel function with value attached.

Adding payable to the fallback function should fix this.