Improvements to RTargetGroup intropsect

Following changes are implemented:

- Allow filtering the output of ShowRtGroupReq by target
- ShowRtGroupSummaryReq lists targets without dependent routes
- ShowRtGroupPeerReq lists all targets for a peer
- Targets in output of summary response are clickable

Change-Id: I2c5661f6414b5335c5498f61fd0922e5da0dd4e5
Closes-Bug: 1382634