Improve files structure

[tisonkun]

Modification:

• Move tools/ci to .github/config
• Rename tools as utils to make it clear for end-users.
• Rename try_cluster to create-cluster aligned with Redis as promote it as a formal utility.
• Move systemd to utils to reduce top-level folders.

Some following engineering improvement thoughts:

• Use cases and images moved to https://github.com/apache/incubator-kvrocks-website, remove the docs folder.
• More README/usage info for utilities (utils).
• Move VERSION file to src folder.
• Replace sed in Dockerfile with command-line arguments supported by Support CLI options for kvrocks server #1037
• Figure out a smaller base image for the Docker image, perhaps https://github.com/GoogleContainerTools/distroless.
• Properly handle NOTICE. Keep a copy of the LICENSE and NOTICE from deps in the licenses folder.

[PragmaTwice]

LGTM