**What changed?**

Added new fields to read and return `start_by_principal`,
`close_by_principal` and `end_by_principal` to users by
`DescribeActivityExecution`.

**Why?**

This is to enable the read path for SAA Principal Attribute task -
https://temporalio.atlassian.net/browse/ACT-1185.

**Server PR**

https://github.com/temporalio/temporal/pull/12550