add replication delay command

[marcosvm]

Related issue: #1266

Description

This PR adds a command to delay replication on a specific instance keeping the current replication threads status.

Please make sure that:

• contributed code is using same conventions as original code

Please make sure the PR passes CI tests. For your information, CI tests the following:

• - code is formatted via gofmt (please avoid goimports)
• - code passes compilation
• - code passes unit tests
• - code passes integration tests with MySQL backend
• - code passes integration tests with SQLite backend
• - There are no orphaned docs/ pages (there's some link in the docs to point to any page)
• - upgrade from previous version (master branch) is successful

[shlomi-noach]

Thank you! This looks good, with a few requests for changes. Please consider adding a delay-replication command in https://github.com/openark/orchestrator/blob/master/resources/bin/orchestrator-client

[marcosvm]

@shlomi-noach I added the modifications you suggested. Thank you for the review.