[dhcp_server] Add dhcp_server container (#14031)

Why I did it
Add dhcp_server ipv4 feature to SONiC.
HLD: sonic-net/SONiC#1282

How I did it
To be clarify: This container is disabled by INCLUDE_DHCP_SERVER = n for now, which would cause container not build.

Add INCLUDE_DHCP_SERVER to indicate whether to build dhcp_server container
Add docker file for dhcp_server, build and install kea-dhcp4 inside container
Add template file for dhcp_server container services.
Add entry for dhcp_server to FEATURE table in config_db.
How to verify it
Build image with INCLUDE_DHCP_SERVER = y to verify:

Image can be install successfully without crush.
By config feature state dhcp_server enabled to enable dhcp_server.

dockers/docker-dhcp-server/cli/show/plugins/show_dhcp_server.py

@@ -0,0 +1,13 @@
+import click
+import utilities_common.cli as clicommon
+
+
+@click.group(cls=clicommon.AliasedGroup, name="dhcp_server")
+def dhcp_server():
+    """show DHCP Server information"""
+    pass
+
+
+def register(cli):
+    # cli.add_command(dhcp_server)
+    pass