Add configuration for http.Agent

[kravets-levko]

Follow-up on #24

Make parameters for http agent configurable by the end user

[timtucker-dte]

Any updates on this?

[sidfarkus]

We could use this feature as well as customers of ours use a HTTPS proxy and we'd like to override the http.Agent to allow us to configure that. Specifically these lines: https://github.com/databricks/databricks-sql-nodejs/blob/main/lib/connection/connections/HttpConnection.ts#L30-L32