How can I create a palette with symbols for jazz harmonic analysis of score ?

I need a palette with symbols like square bracket under two consecutive chords and some curved or straight arrows with filled and outlined heads etc. to annotate a score like jazz analysis do.

Is there any documentation on how to create a palette and create custom symbols for it that can be anchored on the score ? I have software development knowledge (to some extent...) and would like to contribute such a palette but I could find much direction so far...