[fix][admin] Allow defaultNumPartitions for non-partitioned autoTopicCreation override

[ChimdumebiNebolisa]

Fixes #24998

Motivation

The current namespace autoTopicCreation override validation rejects defaultNumPartitions when topicType=non-partitioned. This forces clients and IaC tooling to conditionally omit a field based on topic type, which makes the API less consistent and more error-prone.

Modifications

• Relaxed AutoTopicCreationOverride validation to allow defaultNumPartitions to be set when topicType=non-partitioned (value is accepted and persisted).
• Kept runtime behavior unchanged: defaultNumPartitions is still only used for partitioned auto-creation.
• Updated unit test expectations and added a broker test to verify the value is ignored during non-partitioned topic creation.

Verifying this change

This change added tests and can be verified as follows:

• mvn -pl pulsar-common -Dtest=AutoTopicCreationOverrideTest test
• mvn -pl pulsar-broker -am -Dtest=AdminApi2Test#testAutoTopicCreationOverrideNonPartitionedDefaultNumPartitionsIgnored -Dsurefire.failIfNoSpecifiedTests=false test

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

• Dependencies (add or upgrade a dependency)
• The public API
• The schema
• The default values of configurations
• The threading model
• The binary protocol
• The REST endpoints
• The admin CLI options
• The metrics
• Anything that affects deployment

Documentation

• doc-not-needed

Note: Updated validateOverride to preserve topic type validation and allow defaultNumPartitions for NON_PARTITIONED topics only when the value is null, 0, or 1. Updated unit tests to cover 0, 1, and to reject 2.

[ChimdumebiNebolisa]

Updated validateOverride to keep topic type validation and allow defaultNumPartitions for NON_PARTITIONED only when null, 0, or 1. Updated unit tests to cover 0, 1, and reject 2.

[lhotari]

Updated validateOverride to keep topic type validation and allow defaultNumPartitions for NON_PARTITIONED only when null, 0, or 1. Updated unit tests to cover 0, 1, and reject 2.

Please add this information to the PR description.

[lhotari]

LGTM, thanks for the contribution @ChimdumebiNebolisa