Feat: Supabase GitHub proxy

[martinjagodic]

Adds a new backend that enables caching through Supabase. Significantly speeds up collection list loading.

Features:

• caches folder collections entries to a Supabase table
• extends the GitHub Backend
• reloads only changes files based on checksums
• common cache for all users
• each branch is cached separately - branch column in the DB

Next steps (out of scope of this PR):

• use Supabase auth (replaces Netlify Identity)
• improve entry view loading
• cache single-file collections
• Upon saving an entry and returning to list view, entries should not be reordered

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[martinjagodic]

local_backend doesn't load any entries in cacheable collections - happened in incognito browser, can't reproduce anymore

[martinjagodic]

A problem with titles of subfolders in nested collections sidebar. On https://develop.moc-www.pages.dev/admin/#/collections/upravljanje/filter/organi-obcine (using branch moc-supabase-github-proxy) The title of folder organi-obcine is "Župan" instead of "Organi občine". It is ok on localhost on feat/supabase-github-proxy branch.