fix(pubsub): mark ignore option default for publish flow control

[hongalex]

Make ignore flow control the default option for publisher flow control. In addition, fix bug where default settings were not being respected.

Fixes #5976

[shollyman]

Re-ordering the values via the iota is suspicious to me. If users are using the names consistently it is reasonable, but if they've been setting the int values directly or define their own enum-like things this will potentially cause a behavior change.

[hongalex]

Re-ordering the values via the iota is suspicious to me. If users are using the names consistently it is reasonable, but if they've been setting the int values directly or define their own enum-like things this will potentially cause a behavior change.

Yeah I didn't really want to do this but due to a bug/happenstance this is not a breaking change. There was a bug in the code where we compare the t.PublishSettings.FlowControlSettings.LimitExceededBehavior field (default Block since it's the zero value) to LimitExceededBlock. However, since the default value is actually Ignore, users have been unable to set this to Block.

With this change, Ignore should be the default option both in the DefaultReceiveSettings struct as well with the enum and users will be able to use both Ignore and Block properly.

edit: Also, the iota reordering has to happen. As is, we cannot differentiate between if the user didn't set the LimitExceededBehavior field or if they intentionally want to use Block. If the user doesn't change this field, we need to use the default value (which is Ignore).

[shollyman]

LGTM given the additional context.

[feywind]

Approving on behalf of others not in the groups.