Fixes

The ClientRequest type (alias of RequestOptions) in Client.setDefaultRequest has required field url.

This means, when using Client.setDefaultRequest({ httpsAgent: new https.Agent() }), for example, TypeScript will error with field url is missing.

This PR makes the type partial, so all fields are optional which reflects the actual behaviour.

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