feature: add possibility to replace a participant

[iamgiolaga]

Discussed in #6

^{Originally posted by iamgiolaga November 12, 2022}
Currently, if you need to rename or, in general, replace a specific participant, then you need to remove it and add the new one.
It would be ideal to add a new message handler for a syntax like cambia x con y.

[iamgiolaga]

warning: this could be easily confused with scambia (for teams)

[iamgiolaga]

challenge: shall we implement both cases where we replace somebody as confirmed (✅) and as maybe (❓) ?