Improving regular SSH port forwarding audit logs

[eriktate]

This PR emits some additional events for SSH port forwarding and adds some context around local/remote when possible. The emitted events should look like the following:

• Local port forwarding logs a start and end event per connection.
• Remote port forwarding for the regular SSH server logs a start and end event per forwarding session as well as per connection.
• Remote and local port forwarding for the forward SSH server log an event for everything, but the session-level events do not differentiate between remote/local. There are some small issues with properly capturing event data for the forward server, so I've not included the new events in this PR. I plan on addressing this in a follow up

Every event should contain the remote, local, and target address where applicable. For remote forwarding, session-level events will show the requester as the remote address whereas connection-level events should show the client address initiating the connection.

changelog: Added more granular audit logging surrounding SSH port forwarding

[rosstimothy]

It looks like the events are now being emitted in the right places, though I'm seeing a few things that still need to be addressed.

The logs are spewing the following when emitting events:

ERRO  Attempted to convert dynamic event of unknown type into protobuf event. event_type:port.local events/dynamic.go:483

The web ui is unable to render the forwarding events:

[rosstimothy]

Can you please update the PR title and description to reflect that this is not updating events emitted by the forwarding server and that will happen in the future?

[public-teleport-github-review-bot]

@eriktate See the table below for backport results.

Branch	Result
branch/v15	Failed
branch/v16	Failed
branch/v17	Failed