doc: add http.ClientRequest maxHeadersCount

In http.ClientRequest's doc, add maxHeadersCount as a public property.
And in the description of server's one, change a hyphen to a comma.

PR-URL: https://github.com/nodejs/node/pull/20361
Refs: https://github.com/nodejs/node/pull/20359


Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>