Change Consumer Priority Group State info and fix pinned TTL

[Jarema]

This PR introduces few changes & improvements to Pinned Consumers

Fix pinned TTL timer when its assigned from existing waiting request Until now, we were resetting Pinned TTL only if pin was set on incoming Pull Request, but not when we were pinning an existing waiting request. It also simplifies some logic.

Switch to slice of PriorityGroupState Previously, we were storing just the pinned IDs, but to be more future-proof, this commit will switch approach to store a struct. It also adds PinnedTS which can be useful for debugging pinned consumers.

cc @ripienaar @jnmoyne

Signed-off-by: Tomasz Pietrek tomasz@nats.io

[derekcollison]

Let me know if you want to hold on merge til @ripienaar and/or @jnmoyne have a chance to review as well.

[jnmoyne]

Reviewed and tested the changes and they LGTM