BR add version check at beginning.

[3pointer]

Feature Request

Describe your feature request related problem:

Current not all BR version is compatible with all TiDB version, For example, BR 3.1 is not compatible with TiDB 4.0.

Describe the feature you'd like:

A version check when start BR.

Describe alternatives you've considered:

Use PD to get backup/restore cluster version, if not compatible, then warning in log.

Teachability, Documentation, Adoption, Migration Strategy: