Add Memq Metadata Client

[ArtemTetenkin]

Add Memq Metadata Client
Here's a summary of all the changes:

Files created
psc/src/main/java/com/pinterest/psc/metadata/client/memq/PscMemqMetadataClient.java - The main Memq metadata client implementation extending PscBackendMetadataClient. Since Memq doesn't have a dedicated admin client (unlike Kafka's AdminClient), it uses short-lived MemqConsumer instances for all metadata queries. The implementation:

listTopicRns() - throws UnsupportedOperationException since Memq doesn't support listing all topics
describeTopicUris() - creates a consumer per topic, subscribes, and calls getPartition() to discover partitions
listOffsets() - groups partitions by topic, uses getEarliestOffsets() / getLatestOffsets() based on the requested option
listOffsetsForTimestamps() - groups by topic and uses offsetsOfTimestamps()
listOffsetsForConsumerGroup() - creates a consumer with the target consumer group ID and uses committed() per partition
psc/src/main/java/com/pinterest/psc/metadata/creation/PscMemqMetadataClientCreator.java - The plugin creator class annotated with @PscMetadataClientCreatorPlugin(backend = "memq", priority = 1), following the exact same pattern as PscKafkaMetadataClientCreator. It creates and initializes PscMemqMetadataClient instances and validates Memq topic URIs via MemqTopicUri.validate().

psc/src/main/java/com/pinterest/psc/config/PscMetadataClientToMemqConsumerConfigConverter.java - Config converter that extends PscMetadataClientToBackendMetatadataClientConfigCoverter, mapping PSC metadata client configuration to Memq consumer configs (e.g., PSC_METADATA_CLIENT_ID to ConsumerConfigs.CLIENT_ID).

File modified
psc/src/main/java/com/pinterest/psc/consumer/memq/MemqTopicUri.java - Changed the constructor from package-private to public so it can be used from the com.pinterest.psc.metadata.client.memq package (consistent with how KafkaTopicUri has a public constructor).

[jeffxiang]

this is needed - we'll update MemQ consumer