feature: public namespace support different formats

[dake0805]

What's the purpose of this PR

Add new feature:

• Can create public namespace in different formats, include json, xml, yml, yaml, txt, just like creating a private namespace.
• Public namespace in these formats can be associated correctly.

Discussion

Which issue(s) this PR fixes:

Fixes #2602

Brief changelog

• Remove verify formats of creating public namespace in portal API and front-end
• Add front-end elements to create public namespace in formats
• Add front-end text box to show associated namespace when parent namespace are different with child namespace.

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