doc: announce sched API changes for dynamic config

doc: announce sched API changes for dynamic config

Add deprecation note for making changes in data structures and APIs
in order to allow dynamic configuration of subport bandwidth profile.
These changes are aligned as suggested in the RFC[1].

https://mails.dpdk.org/archives/dev/2020-July/175161.html

Signed-off-by: Savinay Dharmappa <savinay.dharmappa@intel.com>
Acked-by: Jasvinder Singh <jasvinder.singh@intel.com>
Acked-by: Praveen Shetty <praveen.shetty@intel.com>
Acked-by: Sunil Pai G <sunil.pai.g@intel.com>