## What changed?
In most cases, use `metadata.ValueFromIncomingContext` instead of
`metadata.FromIncomingContext` to get grpc metadata. (History client
`StreamWorkflowReplicationMessages` still uses `FromIncomingContext`
because it copies all headers.)
## Why?
`ValueFromIncomingContext` does less allocation when you just need to
access a specific header.
## How did you test it?
existing tests
