Support namespace CRUD

[Venjy]

This closes #137

• Add banner home, cluster and community
• Support namespace listing, creation, and deletion

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (d01e985) 25.91% compared to head (b208599) 24.67%. Report is 20 commits behind head on unstable.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## unstable #149 +/- ## ============================================ - Coverage 25.91% 24.67% -1.25% ============================================ Files 31 42 +11 Lines 2639 3595 +956 ============================================ + Hits 684 887 +203 - Misses 1861 2597 +736 - Partials 94 111 +17 ``` | [Flag](https://app.codecov.io/gh/apache/kvrocks-controller/pull/149/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=apache) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/apache/kvrocks-controller/pull/149/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=apache) | `24.67% <ø> (-1.25%)` | :arrow_down: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=apache#carryforward-flags-in-the-pull-request-comment) to find out more.

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[PragmaTwice]

Could you publish the web app to somewhere (e.g. surge.sh) that we can have a try?

[git-hulk]

@PragmaTwice I have tried it on my side and it looks good.

[PragmaTwice]

Thank you for your contribution!