[Test Gap][RADIUS][Any]Add initial RADIUS test cases

[dt-nexthop]

Test Gap Description

Currently there are no test cases for the RADIUS protocol. Adding a suite of RADIUS tests will be helpful to ensure no regressions occur and basic funtionality works as expected

Test Plan

Initial PR will include:

• Test RADIUS authentication with different MPL
• Test RADIUS statistics
• Test configuring and removing basic RADIUS configuration
• This will also involve setting up a RAIDUS sever in docker ptf - relevent PR: Add freeRADIUS package to docker-ptf  sonic-buildimage#21307

Test environment

These test cases can be used on any sonic-mgmt topology that is running a version that has RADIUS support

Attach files (if any)

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