Use -1 as sentinel value for namespace and topic admin commands

[klevy-toast]

Fixes #1429

Motivation

Use -1 as a sentinel value for all the namespace / topic admin get commands that return an empty body to mean "unset"

Modifications

-1 is the default return for the various get commands:

Namespace Admin Methods

- GetNamespaceMessageTTL / GetNamespaceMessageTTLWithContext
- GetMaxConsumersPerTopic / GetMaxConsumersPerTopicWithContext
- GetMaxProducersPerTopic / GetMaxProducersPerTopicWithContext
- GetMaxConsumersPerSubscription / GetMaxConsumersPerSubscriptionWithContext
- GetOffloadThreshold / GetOffloadThresholdWithContext
- GetOffloadThresholdInSeconds / GetOffloadThresholdInSecondsWithContext
- GetOffloadDeleteLag / GetOffloadDeleteLagWithContext
- GetCompactionThreshold / GetCompactionThresholdWithContext

Topic Admin Methods

- GetMessageTTL / GetMessageTTLWithContext
- GetMaxProducers / GetMaxProducersWithContext
- GetMaxConsumers / GetMaxConsumersWithContext
- GetMaxUnackMessagesPerConsumer / GetMaxUnackMessagesPerConsumerWithContext
- GetMaxUnackMessagesPerSubscription / GetMaxUnackMessagesPerSubscriptionWithContext
- GetCompactionThreshold / GetCompactionThresholdWithContext
- GetMaxConsumersPerSubscription / GetMaxConsumersPerSubscriptionWithContext
- GetMaxMessageSize / GetMaxMessageSizeWithContext
- GetMaxSubscriptionsPerTopic / GetMaxSubscriptionsPerTopicWithContext
- GetDeduplicationSnapshotInterval / GetDeduplicationSnapshotIntervalWithContext

Verifying this change

• Make sure that the change passes the CI checks.

This change added tests and can be verified as follows:

(example:)

• Added new tests for the various commands that were not already covered by tests

Does this pull request potentially affect one of the following parts:

If yes was chosen, please highlight the changes

• Dependencies (does it add or upgrade a dependency): (yes / no)
• The public API: (yes / no)
• The schema: (yes / no / don't know)
• The default values of configurations: (yes / no)
• The wire protocol: (yes / no)

Documentation

• Does this pull request introduce a new feature? (yes / no)
• If yes, how is the feature documented? (not applicable / docs / GoDocs / not documented)
• If a feature is not applicable for documentation, explain why?
• If a feature is not documented yet in this PR, please create a followup issue for adding the documentation