record tidb cluster workload state in status field

[cofyc]

Feature Request

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

At first, we can add a new condition to indicate the tidb cluster is ready or not:

    // TidbClusterReady indicates that the tidb cluster is ready or not.
    // This is defined as:
    // - All statefulsets are up to date (currentRevision == updateRevision).
    // - All PD members are healthy.
    // - All TiDB pods are healthy.
    // - All TiKV stores are up.
    // - All TiFlash stores are up.
    TidbClusterReady TidbClusterConditionType = "Ready"

Describe the feature you'd like:

like conditions in builtin kubernetes workload objects

Describe alternatives you've considered:

Teachability, Documentation, Adoption, Migration Strategy: