[cosmetic]: Change relevant instances of append -> prepend (#632)
[cosmetic]: Change relevant instances of append -> prepend (#632)

* Add option for `RFC7951JSONConfig` to prepend module names only for irefs

I made it clear in the comments that this should be avoided for any standard implementation.

- Improve appmodsJSON doc comments.
- Change appendModuleName and similar names to prependModuleNameIref and similar names.
- Add new field `PrependModuleNameIdentityref` to `RFC7951JSONConfig`.

Tested:

Added test that `PrependModuleNameIdentityref` prepends only for identityrefs.

* Change relevant instances of append -> prepend
openconfig/ygot,openconfig/ygot