Support syslog rate limit configuration for containers and host

[Junchao-Mellanox]

HLD: https://github.com/sonic-net/SONiC/pull/1049

What I did

Support CLIs for syslog rate limit feature

How I did it

Support 4 new CLIs:

1. config syslog rate-limit-host
2. show syslog rate-limit-host
3. config syslog rate-limit-container
4. show syslog rate-limit-container

How to verify it

Unit test

Previous command output (if the output of a command-line utility has changed)

N/A

New command output (if the output of a command-line utility has changed)

Example:
show syslog rate-limit-host
INTERVAL     BURST
----------   --------
500          50000
show syslog rate-limit-container
SERVICE    INTERVAL     BURST
--------   ----------   --------
bgp        500          N/A
snmp       300          20000
swss       2000         12000
show syslog rate-limit-container bgp
SERVICE    INTERVAL     BURST
--------   ----------   --------
bgp        500          5000

[lgtm-com[bot]]

This pull request introduces 3 alerts when merging 238bd6755fcc1ac90daf8eac29c115beb40c1b53 into c2841b8ced4f0257a59b6af16e41990cc8de55d1 - view on LGTM.com

new alerts:

• 3 for Unused import

[Junchao-Mellanox]

Hi @mkeda, I have fixed/replied all comments. Would you please review the new changes?

[Junchao-Mellanox]

Hi @saiarcot895, thanks for the comments, I have fixed it, could you please continue reviewing?