Add workflow rules (#7437)

## What changed?
<!-- Describe what has changed in this PR -->
Add implementation to the following API:
* CreateWorkflowRule
* DescribeWorkflowRule
* DeleteWorkflowRule
* ListWorkflowRules

Add initial rule implementation - activity will be paused on activity
Retry.
Add functional test for that.

All functions are behind feature flag.

## Why?
<!-- Tell your future self why have you made these changes -->
Part of workflow rules work.

## How did you test it?
<!-- How have you verified this change? Tested locally? Added a unit
test? Checked in staging env? -->
Add unit test.
Add func test.

## Potential risks
<!-- Assuming the worst case, what can be broken when deploying this
change to production? -->
N/A

Author: ychebotarev