[type:feat] Shenyu client namespace supports

[moremind]

about #5324

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• You have read the contribution guidelines.
• You submit test cases (unit or integration tests) that back your changes.
• Your local test passed ./mvnw clean install -Dmaven.javadoc.skip=true.

[xcsnx]

If the user does not fill in the namespaceId, won't the client side provide a default namespaceId?

[moremind]

If the user does not fill in the namespaceId, won't the client side provide a default namespaceId?

exist default ns id

[xcsnx]

If the user does not fill in the namespaceId, won't the client side provide a default namespaceId?

exist default ns id

okk