make doc site toggle between options and composition api just like vue site

[laoshaw]

What problem is this solving

it's hard to follow pinia's document due to the mixing of options-api and composition-api, also the composition api is not vue3.2 ready(script-setup)

Proposed solution

make the doc switchable between options and composition mode

Describe alternatives you've considered

the same way vue's doc site

[posva]

Added to #829 but unsure if this is feasible/worth since it's not exactly like in Vue docs.

It was already there.