Add playground integration

[ferranbt]

📝 Summary

This PR implements and integration test using the builder-playground:

• It creates a playground.rs utility library to interact with the playground. In this first iteration, most of the variables (e.g. private keys, urls, etc...) are hardcoded.
• It creates a simple integration test that ensures that a transaction sent to the EL gets mined by the rbuilder and included on the block through mev-boost-relay.
• It runs the integration test in CI after the unit tests have passed.

The integration test works directly with the rbuilder compiled binary.

💡 Motivation and Context

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✅ I have completed the following steps:

• Run make lint
• Run make test
• Added tests (if applicable)

[github-actions]

Benchmark results for 1172987

Report: https://flashbots-rbuilder-ci-stats.s3.us-east-2.amazonaws.com/benchmark/1172987-21fea73/report/index.html

Date (UTC)	2024-08-05T17:45:28+00:00
Commit	117298711f27a0fbef18b20e3a3485d35333a4a1
Base SHA	21fea738fc06cf0832a5cedbcc49eb9211c3a68c

Significant changes

None

[metachris]

is this step needed? couldn't you directly upload the folder as artifact without moving?

[metachris]

would be ideal if we could put the local chain data into ~/.builder-playground/... where the other builder playground stuff is located in. that way there could be a single example config that works for everyone.