Add ability to set default option on SendableChooser without passing in the value

[ishan-karmakar]

Is your feature request related to a problem? Please describe.
In some cases, we want to be able to switch the default value of the sendable chooser after adding all of the values into the chooser.

Describe the solution you'd like
An overload can be added to SetDefaultOption that doesn't take in a value and doesn't call AddOption (simply sets the default choice string)

Describe alternatives you've considered
Since SendableChooser requires the type to be copy constructible, it is possible to just pass in the same value and overwrite it, but it feels jank.

[PeterJohnson]

Fixed in #7773’s replacement for SendableChooser (Selectable).