Fix/DF-20791 legacy

[mmcallister-cll]

Closes #DF-20791

Description

Fixing eth-balance update to allow proper ethers provider selection for "chainId": "mainnet" as used in several other feeds

Changes

• fixed provider selection logic

Steps to Test

1. yarn test eth-balance
2. sanity check existing calls with chainId: "string" use configured default RPC provider

Quality Assurance

• If a new adapter was made, or an existing one was modified so that its environment variables have changed, update the relevant infra-k8s configuration file.
• If a new adapter was made, or an existing one was modified so that its environment variables have changed, update the relevant adapter-secrets configuration file or update the soak testing blacklist.
• If a new adapter was made, or a new endpoint was added, update the test-payload.json file with relevant requests.
• The branch naming follows git flow (feature/x, chore/x, release/x, hotfix/x, fix/x) or is created from Jira.
• This is related to a maximum of one Jira story or GitHub issue.
• Types are safe (avoid TypeScript/TSLint features like any and disable, instead use more specific types).
• All code changes have 100% unit and integration test coverage. If testing is not applicable or too difficult to justify doing, the reasoning should be documented explicitly in the PR.

[changeset-bot]

🦋 Changeset detected

Latest commit: 58eed1b

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 3 packages

Name	Type
@chainlink/eth-balance-adapter	Minor
@chainlink/proof-of-reserves-adapter	Patch
@chainlink/renvm-address-set-adapter	Patch

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