Add support for IOS-XR configuration comments

[aedwardstx]

Add support for IOS-XR configuration comments

router isis backbone
 set-overload-bit on-startup 180
 is-type level-2-only
 ! ISIS network number should be encoded with 0-padded loopback IP
 ! example:
 ! example: 
 net 49.0001.1921.2022.0222.00

I'm thinking the comments should be a property of the configuration line just below the comment lines.

How to remove comments:
https://supportforums.cisco.com/t5/xr-os-and-platforms/cisco-ios-xr-remove-comment/td-p/2546154