[feature](restapi) add global session variables restapis

[heguanhui]

• batch set for variables
• batch get get for variables
• batch unset for variables
• unset all variables

Release note

support restapis to fullfil functions like show global variables like xxx

Check List (For Author)

• Test

  • [ ] Regression test
  • [ ] Manual test (add detailed scripts or steps below)

• Behavior changed:

  • [ ] No.

• Does this need documentation?

  • [ ] Yes.

Check List (For Reviewer who merge this PR)

• [ ] Confirm the release note
• [ ] Confirm test cases
• [ ] Confirm document
• [ ] Add branch pick label

[hello-stephen]

Thank you for your contribution to Apache Doris. Don't know what should be done next? See How to process your PR.

Please clearly describe your PR:

1. What problem was fixed (it's best to include specific error reporting information). How it was fixed.
2. Which behaviors were modified. What was the previous behavior, what is it now, why was it modified, and what possible impacts might there be.
3. What features were added. Why was this function added?
4. Which code was refactored and why was this part of the code refactored?
5. Which functions were optimized and what is the difference before and after the optimization?