CI: Add Ecosystem tests

[bkchr]

This adds the ecosystem tests as a CI job.

• Does not require a CHANGELOG entry

[bkchr]

@xlc any idea why the ecosystem tests are failing: https://github.com/polkadot-fellows/runtimes/actions/runs/12518886514/job/34922591260?pr=521 ?

[xlc]

The error is Error handling request: 'RpcError: -32008: Response is too big: Exceeded max limit of 1048576 so it is requesting some big value from RPC and failed. There are a few similar intermittent errors in the nightly runs of the ecosystem tests and I haven't got the chance to investigate on exactly what state caused the error and why it is only an Intermittent error (rerun fixes the error most of the time).
Will spend some time on this. Meanwhile, I will suggest setup some retry logic. e.g. https://github.com/open-web3-stack/polkadot-ecosystem-tests/blob/f6b76c9201dfca0c1f95e14840ccfed2029efd02/.github/workflows/update-known-good.yml#L105

[bkchr]

The error is Error handling request: 'RpcError: -32008: Response is too big: Exceeded max limit of 1048576 so it is requesting some big value from RPC and failed. There are a few similar intermittent errors in the nightly runs of the ecosystem tests and I haven't got the chance to investigate on exactly what state caused the error and why it is only an Intermittent error (rerun fixes the error most of the time).

Maybe we need a dedicated RPC server with a higher response limit.

[bkchr]

What is weird is that it already fails on getting the runtime version:

getRuntimeVersion(at?: BlockHash): RuntimeVersion:: -32603: Internal RpcError: -32008: Response is too big: Exceeded max limit of 1048576

[xlc]

it is possible to set rpc endpoints via env vars and we can use github action secrets to avoid expose internal rpcs to public

[bkchr]

What is also weird is that the default max response size is 15MIB. Meaning they have decreased the size quite a lot?