feat: Add support for file-based snippets in Studio

[ivasilov]

What kind of change does this PR introduce?

This PR adds support for file-based SQL snippets in Studio.

What is the current behavior?

The snippets are saved in browser storage and dissapear on refresh.

What is the new behavior?

The snippets have almost feature-parity with the snippets on the platform variant except:

• favourite snippets
• shared snippets
• rename a folder

Additional context

Should be merged before supabase/supabase#41112.

[coveralls]

Pull Request Test Coverage Report for Build 20456686970

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

• For more information on this, see Tracking coverage changes with pull request builds.
• To avoid this issue with future PRs, see these Recommended CI Configurations.
• For a quick fix, rebase this PR at GitHub. Your next report should be accurate.

Details

• 4 of 4 (100.0%) changed or added relevant lines in 1 file are covered.
• 5 unchanged lines in 1 file lost coverage.
• Overall coverage decreased (-0.01%) to 56.1%

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Files with Coverage Reduction	New Missed Lines	%
internal/gen/keys/keys.go	5	12.9%

Totals
Change from base Build 20454832107:	-0.01%
Covered Lines:	6833
Relevant Lines:	12180

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💛 - Coveralls