fix: typings for Client.setDefaultRequest

[brettwillis]

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

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

[brettwillis]

Also, why are issues disabled on this repo?

[ank1995it]

Facing this sonar issue : Cross-site Request Forgery (CSRF) [High Severity][https://security.snyk.io/vuln/SNYK-JS-AXIOS-6032459] in axios@0.26.1 introduced by @sendgrid/mail@7.7.0 > @sendgrid/client@7.7.0 > axios@0.26.1