pim-msdp: part-4: cli cleanup

pim-msdp: part-4: cli cleanup

1. Add support for mesh-group based configuration that is easy to apply
via automation. The older per-peer configuartion is temporarily hidden
and will be cleaned up later.
Sample config -
ip msdp mesh-group cumulus source 100.1.1.4
ip msdp mesh-group cumulus member 100.1.1.5
ip msdp mesh-group cumulus member 100.1.1.6

2. Added support for detail peer and sa-cache displays. Along with
filter keys.

3. Add json output for all the msdp displays.

With this commit basic support for anycast-RP with MSDP (in numbered
network is complete). Unnumbered support will be added separately.

Ticket: CM-13306

Signed-off-by: Anuradha Karuppiah <anuradhak@cumulusnetworks.com>
Acked-by: Donald Sharp <sharpd@cumulusnetworks.com>