[Nexthop][fboss2-dev] Save the config commands to CLI metadata and in session commit.

[benoit-nexthop]

Pre-submission checklist

• I've ran the linters locally and fixed lint errors related to the files I modified in this PR. You can install the linters by running pip install -r requirements-dev.txt && pre-commit install
• pre-commit run

Summary

Now every config command is saved in the CLI session metadata so we can
easily tell what commands were used in a given session. The metadata is
now also saved along the config when we commit the session. A future
commit will make rollback also rely on this metadata to decide whether
or not to restart the agent.

Note: this change is part of a series, the previous one is #805.

Test Plan

New unit tests added.

Sample usage

[admin@fboss101 ~]$ ~/benoit/fboss2-dev config interface eth1/1/1 description this is a test.
Successfully set description for interface(s) eth1/1/1
[admin@fboss101 ~]$ ~/benoit/fboss2-dev config interface eth1/1/1 mtu 1500
Successfully set MTU for interface(s) eth1/1/1 to 1500
[admin@fboss101 ~]$ ls -l ~/.fboss2/
total 216
-rw-r--r-- 1 admin admin 213174 Jan 13 13:00 agent.conf
-rw-r--r-- 1 admin admin    141 Jan 13 13:00 conf_metadata.json
[admin@fboss101 ~]$ cat ~/.fboss2/conf_metadata.json 
{
  "action": {},
  "commands": [
    "config interface eth1/1/1 description this is a test.",
    "config interface eth1/1/1 mtu 1500"
  ]
}
[admin@fboss101 ~]$ ~/benoit/fboss2-dev config session commit
Config session committed successfully as r6 and config reloaded.
[admin@fboss101 ~]$ ls -l /etc/coop/cli/
total 1292
-rw-r--r-- 1 root  root  213185 Jan 13 12:52 agent-r1.conf
-rw-r--r-- 1 admin admin 213194 Jan 13 12:56 agent-r2.conf
-rw-r--r-- 1 admin admin    108 Jan 13 12:56 agent-r2.metadata.json
-rw-r--r-- 1 admin admin 213185 Jan 13 12:56 agent-r3.conf
-rw-r--r-- 1 admin admin     99 Jan 13 12:56 agent-r3.metadata.json
-rw-r--r-- 1 admin admin 213185 Jan 13 12:58 agent-r4.conf
-rw-r--r-- 1 admin admin     80 Jan 13 12:58 agent-r4.metadata.json
-rw-r--r-- 1 admin admin 213185 Jan 13 12:58 agent-r5.conf
-rw-r--r-- 1 admin admin     80 Jan 13 12:58 agent-r5.metadata.json
-rw-r--r-- 1 admin admin 213174 Jan 13 13:00 agent-r6.conf
-rw-r--r-- 1 admin admin    141 Jan 13 13:00 agent-r6.metadata.json
[admin@fboss101 ~]$ cat /etc/coop/cli/agent-r6.metadata.json 
{
  "action": {},
  "commands": [
    "config interface eth1/1/1 description this is a test.",
    "config interface eth1/1/1 mtu 1500"
  ]
}