SNOW-1868467: support adding custom headers on each request

[bpackter]

What is the current behavior?

There is no options to add custom headers on each snowflake request (login, query, telemetry, heartbeat etc..)
This is needed in our case because we are calling snowflake from proxy and proxy enforce us to add jwt in some custom header.

What is the desired behavior?

1. add an option to add map of custom headers in session coonig.
2. make sure headers are added on each request

How would this improve snowflake-jdbc?

Make this more robust for customers, especially when using proxy.

References, Other Background

[sfc-gh-dszmolka]

hi - thank you for raising this request and also appreciate suggesting a possible solution for it (the PR). The team will review after the holiday season.

If this capability is critical for your business for any reason, I would also recommend reaching out to your Snowflake Account Team and officially request the feature - this can sometimes speed up prioritization.