Smartswitch support for container checker and frr

[rameshraghupathy]

Why I did it

Some sonic-mgmt container-checker tests fail on the smartswitch platform as the containers running on smartswitch are different than the fixed chassis. Similarly some frr tests fail on smartswitch platform as we have chassisdb in smartswitch, the frr code takes the wrong code path related to modular chassis.

Note: #18676 was created first and however that was created using 202311 branch and this logic is not needed there.

How I did it

Created a function is_smartswitch() similart to is_supervisor() using the presence of "DPUS" in platform.json file. Used this function to differentiate smatswitch chassis from modular chassis. Similarly in frr used the same logic to create an env variable to differentiate smatswitch chassis from modular chassis.

How to verify it

Run the sonic-mgmt frr tests and any test. They all pass with this fix.

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

None

• [ ] 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)