Http admin part2 (#2002)

### What problem does this PR solve?

_HTTP APIs for admin mode: set node role, list node variables, list node
configs, show node variable_

Issue link: #1937 

### Type of change

- [x] New Feature (non-breaking change which adds functionality)
- [x] Documentation Update

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Signed-off-by: vsian <[email protected]>

Author: vsian