Why I did it
https://github.com/Azure/SONiC/blob/master/doc/vxlan/Overlay%20ECMP%20with%20BFD.md
From the design, need to advertise the route with community string, the PR is to implement this.
How I did it
To use the route-map as the profile for the community string, all advertised routes can be associated with one route-map.
Add one file, mangers_rm.py, which is to add/update/del the route-map. Modified the managers_advertise_rt.py file to associate profile with IP route.
The route-map usage is very flexible, by this PR, we only support one fixed usage to add community string for route to simplify this design.
How to verify it
Implement new unit tests for mangers_rm.py and updated unit test for managers_advertise_rt.py.
Manually verified the test case in the test plan section, will add testcase in sonic-mgmt later. Azure/sonic-mgmt#5581
