deps: update consul-server-connection-manager

[mikemorris]

This resolves test flakiness issues caused by the un-threadsafety of registering a gRPC balancer in NewWatcher rather than an init() function. This didn't cause problems in actual deployments, but could happen when in our test suite when multiple calls to NewWatcher happened concurrently.

Changes proposed in this PR:

• Updates to a new version of consul-server-connection-manager which removes the gRPC custom balancer implementation and switches to the default pick_first balancer.
• Removes the now-unnecessary globalWatcherMutex (added in Integrate consul-server-connection-manager library #449)
• Removes an unneeded context cancellation call from the client.WatchServers method which was responsible for a race condition occurring infrequently on timeouts, particularly from the discovery-error unit test.
  • This context cancellation was already handled by the caller at

    consul-api-gateway/internal/commands/exec/exec.go

    Line 85 in 874f324

    defer sessionCancel()

How I've tested this PR:

Research and discussion on upstream implementation with @kisunji and @pglass, testing hashicorp/consul-server-connection-manager#28 as a dependency locally and in CI. Thanks for the help in tracking down these issues!

How I expect reviewers to test this PR:

The CI unit tests should stop being flaky.

Checklist:

• Tests added
• CHANGELOG entry added

  Run make changelog-entry for guidance in authoring a changelog entry, and
  commit the resulting file, which should have a name matching your PR number.
  Entries should use imperative present tense (e.g. Add support for...)

[nathancoleman]

Thanks for knocking this out!