[dhcp_server] Fix config cli plugin missing parameter db

[w1nda]

Why I did it

1. The dhcp_server command didn't receive the db passed by @clicommon.pass_db correctly and there is no unit test case covering this.
2. The feature state checking logic in dhcp_server command won't run when there is no sub-command provided.

Work item tracking

• Microsoft ADO (number only): 27384157

How I did it

1. Add the missing parameter and write UT to test it,
2. Add parameter invoke_without_command=True to make sure the command would check feature state no matter if sub-command provided.
3. Because I add the invoke_without_command=True, so I need to explicitly print help message and exit when there is no sub-command provided.

How to verify it

Write UT to capture the issue before fixing it.
Write UT to check the feature state checking logic.

Which release branch to backport (provide reason below if selected)

• 201811
• 201911
• 202006
• 202012
• 202106
• 202111
• 202205
• 202211
• 202305

Tested branch (Please provide the tested image version)

Description for the changelog

Link to config_db schema for YANG module changes

A picture of a cute animal (not mandatory but encouraged)

[w1nda]

Hi @yxieca, cloud you help merge this PR? thank you.