Add an option to disable namespace checker's replica relocation

[nanne007]

Please answer these questions before submitting your issue. Thanks!

1. What did you do?
   Replica checker got options(like DisableLocationReplacement, DisableRemoveExtraReplica) to disable parts of it's features.
   Namespace checker should have have a similar one to enable more robust namespace scheduling.
   If it's wanted, I will give a pr on it, which is just a mirror of schedule: add options to disable replica checker features #1140.

2. What did you expect to see?

3. What did you see instead?

4. What version of PD are you using (pd-server -V)?

[disksing]

@lerencao Yes, we do need it! Looking forward to your updates :)

[nanne007]

Closing it as PR was merged already.