Add host label at deploy stage by default

[Win-Man]

Feature Request

Is your feature request related to a problem? Please describe:

I deployed a cluster which had 2 tikv instances on one server and didn't add the label config. Then one of the servers crashed. It result some regions can't access and may be some data lost.

Describe the feature you'd like:

I suggest tiup could add host label config when deploy a cluster. It's better to add an options like --no-lables to decide not to add host label config. --no-lables should be false by default.

But there are still some scenarios need to be considered:

• If user config the labels in topology.yaml, tiup should use the user's config.
• If user upgrade from previous version, It should add lables or not.

Describe alternatives you've considered:

Alert a warning message if users deploy a cluster which has more than 2 instances on one server and don't add lables config.

Teachability, Documentation, Adoption, Migration Strategy: