isisd, yang, doc: combine config cmd for SRGB+SRLB

isisd, yang, doc: combine config cmd for SRGB+SRLB

when changing both ranges at the same time the order of the commands
matters, as we need to make sure that the intermediate state is valid.
This represents a problem when pushing configuration via frr-reload.
To fix this, the global-block command was extended to optionally
allow setting the local-block range as well. The local-block command
is deprecated with a 1-year notice.

Signed-off-by: Emanuele Di Pascale <emanuele@voltanet.io>