Add command of subscription

[WanYixian]

Info

• Description

  • Add command of subscription.

• Notes

  • [ Include any supplementary context or references here. ]

• Related code PR

  • feat(frontend): Add Create subscription in frontend risingwave#14831
  • feat(frontend): support cursor. risingwave#15180

• Related doc issue

  Resolves Doc: feat(frontend): Add Create subscription in frontend #2129
  Resolves Document: feat(frontend): support cursor. #2084

For reviewers

• Preview

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• Key points

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Before merging

• I have checked the doc site preview, and the updated parts look good.

• I have acquired the approval from the owner (and optionally the reviewers) of the code PR and at least one tech writer (CharlieSYH, emile-00, & hengm3467).

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[ShanlanLi]

LGTM