MaxAckPending vs pending limits

[scottf]

Overview

Change clients to have the behavior described in the Go Client PR 920

When calling js.Subscribe() (or equivalent) and the library ended-up
creating the JS consumer, a MaxAckPending was set to a very high
value in some cases. We now let the server pick the default if the
value is not explicitly set by the user.
The NATS subscription pending limits are set in a way to ensure
that the subscription can store at least the max ack pending value.

Clients and Tools

• Go @piotrpio
• Java @scottf
• JavaScript @aricart (N/A - js client doesn't default max_ack_pending)
• .Net @scottf
• C @levb
• Python @wallyqs
• Ruby @wallyqs
• Rust @Jarema @caspervonb

Other Tasks

• docs.nats.io updated @jnmoyne
• Update ADR to Implemented
• Update client features spreadsheet

Client authors please update with your progress. If you open issues in your own repositories as a result of this request, please link them to this one by pasting the issue URL in a comment or main issue description.