Geo: Add setting to adjust replication lag threshold

Problem to solve

We tell users about replication lag:

in the banner on the secondary UI.
in Git push/pull messages.
for each secondary node in Admin Area > Geo > Nodes.
in rake geo:status.

Admins would probably like a setting that hides replication lag messages when lag is below a configurable threshold.

From https://gitlab.com/gitlab-org/gitlab-ee/issues/9195#note_212827883:

in the spirit of making this configurable, we can aim for a default of only announcing a replication lag if bigger than CONFIGURED_TIME (some may find 30 seconds fine, other will want to be notified if least 10 minutes away), etc. This should be specific to each geo node... so a node in a remote location with unreliable link can default to a bigger latency limit, while a closer one would use a smaller amount of time.

Intended users

Further details

Proposal

Add an Admin Area setting that hides replication lag messages when lag is below a configurable threshold.

Geo: Add setting to adjust replication lag threshold

Problem to solve

Intended users

Further details

Proposal

Permissions and Security

Documentation

Testing

What does success look like, and how can we measure that?

What is the type of buyer?

Links / references