chore: fix op-rbuilder devnet docs

[danyalprout]

📝 Summary

Update the op-rbuilder devnet documentation:

• Update it to use the builder-playground
• Various fixes (e.g. remove optimism feature, use fully qualified docker image so it pulls automatically)

✅ I have completed the following steps:

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

[therustmonk]

The only devnet workflow that worked for me. At least the playground and op-rbuilder started sucessfully. Thanks 🙏

[squadgazzz]

With this approach, I am getting WARN Failed to add builder transaction err=evm execution error: transaction validation error: lack of funds (0) for max fee (1329054756499) from the rbuilder side. If the account needs to be funded manually, could you add this to the readme?

[danyalprout]

@squadgazzz are you using this PR for your local builder-playground?

Currently the default builder playground setup doesn't fund the L2 addresses. I don't want to add this to the readme, as I'm hoping it's temporary until it's merged

[therustmonk]

Perfect 👍

[squadgazzz]

Does it work correctly for you? The run gets stuck

opening DB at /Users/squadgazzz/.contender/contender.db
No private keys provided. Using default private keys.
sending funding txs (1 account)...
waiting for funding tasks to finish...
funding account 0x1E0BC2B8ae3A99760bF83588DA2b4Da649D71E5C with user account 0xf39Fd6e51aad88F6F4ce6aB8827279cffFb92266. tx: 1b454a47f62cd11b27ea513b81dfc8507bd366913ba9b809abbf4cdbb4537237