[Feature]: Add 'insert'/'push' operations to shell builder

[MrPicklePinosaur]

What would you like to see added?

Currently if plugins would like to add aliases or keybindings during the init process, they would have to replace all the existing aliases/keybindings since with_aliases will replace all the existing aliases. We should create new functions called push_alias or insert_alias that allow us to insert single aliases