Allow set a function for joinLastRow parameter

[esindger]

In some complicated cases I need to display a button on the same or on the next row depending on context. Now the joinLastRow parameter has boolean type and it's impossible to set value dynamically.

It would be nice if this parameter has ContextPathFunc<Context, boolean> type (the same as hide parameter).

[EdJoPaTo]

Interesting idea. Not sure if that's easy or messy to add. I will look into it when I find the time.

[EdJoPaTo]

The joinLastRow parameter is used on startup to create the keyboard structure. It is not used afterwards. Which means… refactoring that will be messy / not as simple.

https://github.com/EdJoPaTo/telegraf-inline-menu/blob/ff9823cac16dd646e412669ba3aa28a4d3203bf1/source/keyboard.ts#L37-L46