fix(sidebar): Update SIDEBAR_COOKIE_NAME

[firebed]

Change SIDEBAR_COOKIE_NAME to sidebar_state as mentioned in #106.

[taylorotwell]

I'm so confused by all this sidebar state cookie stuff. Why does this not match the middleware?

[firebed]

The actual issue lies in shadcn's sidebar utils.ts and by extension in vue-starter-kit's utils.ts
Shadcn uses sidebar:state (by mistake) and laravel's middleware uses sidebar_state, so they don't match and this causes the sidebar to always lose it's open/close state after navigation.

This is a known issue and shadcn has already fixed the react version, but the vue version remains problematic.
react-starter-kit also uses sidebar_state sidebar.tsx