[api] Add schema to vercel.json

[dferber90]

Related Issues

• https://twitter.com/vercel_changes/status/1489608976291483653
• https://vercel.com/changelog/schema-autocomplete-and-validation-for-vercel-json

📋 Checklist

Tests

• The code changed/added as part of this PR has been covered with tests
• All tests pass locally with yarn test-unit

Code Review

• This PR has a concise title and thorough description useful to a reviewer
• Issue from task tracker has a link to this PR

[codecov]

Codecov Report

Merging #7394 (d12af5a) into main (2402db9) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main    #7394   +/-   ##
=======================================
  Coverage   49.45%   49.45%           
=======================================
  Files         134      134           
  Lines        5381     5381           
  Branches     1350     1350           
=======================================
  Hits         2661     2661           
+ Misses       2712     2707    -5     
- Partials        8       13    +5     

Impacted Files	Coverage Δ
packages/cli/src/util/index.ts	7.56% <0.00%> (ø)
packages/cli/src/util/dev/server.ts	59.42% <0.00%> (ø)
packages/cli/src/util/output/error.ts	31.25% <0.00%> (ø)
packages/cli/src/commands/deploy/index.ts	20.05% <0.00%> (ø)
packages/cli/src/util/deploy/process-deployment.ts	10.25% <0.00%> (ø)

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