This commit pushes the primary term into the replication tracker. This
is a precursor to using the primary term to resolving ordering problems
for retention leases. Namely, it can be that out-of-order retention
lease sync requests arrive on a replica. To resolve this, we need a
tuple of (primary term, version). For this to be, the primary term needs
to be accessible in the replication tracker. As the primary term is part
of the replication group anyway, this change conceptually makes sense.

* master:
  Remove types from watcher docs (elastic#38002)
  Add test coverage for Painless general casting of boolean and Boolean (elastic#37780)
  Fixed test bug, lastFollowTime is null if there are no follower indices.
  Add ECS schema for user-agent ingest processor (elastic#37727) (elastic#37984)
  Extract TransportRequestDeduplication from ShardStateAction (elastic#37870)
  Expose retention leases in shard stats (elastic#37991)

…r-primary-term

* elastic/master:
  Mute failing date index name processor test
  Reenable BWC testing after retention lease stats (elastic#38062)
  Move watcher to use seq# and primary term for concurrency control (elastic#37977)
  ILM setPriority corrections for a 0 value (elastic#38001)
  Temporarily disable BWC for retention lease stats (elastic#38049)
  Skip Shrink when numberOfShards not changed (elastic#37953)
  Add dispatching to `HandledTransportAction` (elastic#38050)
  Update httpclient for JDK 11 TLS engine (elastic#37994)
  Reduce flaxiness of ccr recovery timeouts test (elastic#38035)
  Fix ILM status to allow unknown fields (elastic#38043)
  Fix ILM Lifecycle Policy to allow unknown fields (elastic#38041)
  Update verify repository to allow unknown fields (elastic#37619)
  [ML] Datafeed deprecation checks (elastic#38026)
  Deprecate minimum_master_nodes (elastic#37868)