feat: add a timeout options to RequestClient that creates a custom https agent

[benweissmann]

Fixes

This PR improves handling of timeouts and axios options in RequestClient. It:

• Accepts a new timeout option to the RequestClient constructor
• Constructs a custom https Agent with the timeout applied. This ensures that timeouts are applied both at the socket level, and at the request/response level. See: Allow a connect timeout to be specified axios/axios#1739
• Moves construction of the HttpsProxyAgent to the constructor to avoid creating a new agent for each request
• Creates an axios instance rather than mutating axios defaults

Checklist

• I acknowledge that all my contributions will be made under the project's license
• I have made a material change to the repo (functionality, testing, spelling, grammar)
• I have read the Contribution Guidelines and my PR follows them
• I have titled the PR appropriately
• I have updated my branch with the main branch
• I have added tests that prove my fix is effective or that my feature works
• I have added the necessary documentation about the functionality in the appropriate .md file
• I have added inline documentation to the code I modified

If you have questions, please file a support ticket, or create a GitHub Issue in this repository.

[rakatyal]

Thanks for the contribution, changes look good!