[dhcp_server] Add dhcpservd to dhcp_server container

[yaqiangz]

Depends on: #16548

Why I did it

Part implementation of dhcp_server. HLD: sonic-net/SONiC#1282.
Add dhcpservd to dhcp_server container.

Work item tracking

• Microsoft ADO (number only): 25093520

How I did it

1. Add installing required pkg (psutil) in Dockerfile.
2. Add copying required file to container in Dockerfile (kea-dhcp related and dhcpservd related)
3. Add critical_process and supervisor config.
4. Add support for generating kea config (only in dhcpservd.py) and updating lease table (in dhcpservd.py and lease_update.sh)

How to verify it

1. Build image with setting INCLUDE_DHCP_SERVER to y and enabled dhcp_server feature after installed image, container start as expected.
2. Enter container and found that all processes defined in supervisor configuration running as expected.
3. Kill processes defined in critical_processes, container exist.

unit test

========================================== test session starts ==========================================
platform linux -- Python 3.9.2, pytest-6.0.2, py-1.10.0, pluggy-0.13.0
rootdir: /sonic/src/sonic-dhcpservd, configfile: setup.cfg, testpaths: tests
plugins: pyfakefs-5.2.4, cov-2.10.1
collected 26 items                                                                                      

tests/test_dhcp_cfggen.py .........                                                               [ 34%]
tests/test_dhcp_lease.py .....                                                                    [ 53%]
tests/test_dhcp_server_utils.py ........                                                          [ 84%]
tests/test_dhcpservd.py ....                                                                      [100%]Clearing the cache


----------- coverage: platform linux, python 3.9.2-final-0 -----------
Name                             Stmts   Miss Branch BrPart     Cover   Missing
-------------------------------------------------------------------------------
dhcpservd/dhcp_cfggen.py           170     16     72      1    92.98%   49-66, 149-153, 239->241, 241
dhcpservd/dhcp_server_utils.py      37      3     14      0    94.12%   35, 55-56
dhcpservd/dhcp_lease.py             96      3     30      4    94.44%   59->61, 61, 62->63, 63, 75->77, 113->135, 154
dhcpservd/dhcpservd.py              31      1      4      0    97.14%   49
-------------------------------------------------------------------------------
TOTAL                              334     23    120      5    93.83%

Required test coverage of 80.0% reached. Total coverage: 93.83%

========================================== slowest 5 durations ==========================================

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)

[yaqiangz]

/azpw run Azure.sonic-buildimage

[mssonicbld]

/AzurePipelines run Azure.sonic-buildimage

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[yaqiangz]

@yxieca Could you pls help to merge this PR?