feat: test production gateways

[laurentsenta]

Contributes to #104

Add tooling to run tests over multiple gateways & merge the outputs into a single dashboard. This is using a few arbitrary production gateways for now.

• merges fixtures are now a single car v1 with a single root (makes it compatible with web3.storage)
• add test-prod-e2e CI test
  • upload fixtures to web3.storage
  • run gateway conformance test suite on a few (arbitrary) gateways
  • aggregate results & generate dashboard
• generate a badge
• patch add-to-web3 chore(deps): bump actions/core to 1.10.0 storacha/add-to-web3#86

Example of output: https://github.com/singulargarden/gateway-conformance/actions/runs/5680836848
Example of markdown: https://github.com/laurentsenta/gateway-conformance/blob/main/README.md (it links to ipfs/gateway-conformance, hence the gray status for now)

follow-up

• Implement a similar test for dev gateways (see Test production gateways #104 (comment))
• tweak the production gateways we want to test and the specs we cover

[laurentsenta]

Example of output: https://github.com/ipfs/gateway-conformance/actions/runs/5656544133/attempts/1#summary-15324286314
Example of markdown: https://github.com/laurentsenta/gateway-conformance/blob/main/README.md (it links to ipfs/gateway-conformance, hence the gray status for now)

[laurentsenta]

Marking this PR as ready for review, it lays down the tooling to generate dashboards for production and dev gateways.