Update the HttpAgent and HttpAgents Schema of AxiosRequestConfig

Section/Content To Improve

The Schema is mentioned in node js documentation https://nodejs.org/api/http.html#new-agentoptions in this link. we can improve documentation.

Suggested Improvement

https://github.com/axios/axios/pull/5492

I create a PR regardting this issue.

• This PR contains the update of HttpAgent and HttpAgents type in AxiosRequestConfig of index.d.ts to improve the suggestion made by typescript.
• It is not a breaking change or changes in test cases required.

Relevant File(s)

index.d.ts File minor change mentioned in above PR