fix: Optimize Synchronization Interval Descriptions.

Created by: serenashe

Signed-off-by: serenashe serenashe@kubesphere.io

What type of PR is this?

/kind documentation

What this PR does / why we need it:

Optimize UI decriptions.

Which issue(s) this PR fixes:

Fixes #2569 (closed)

Special notes for reviewers:

Does this PR introduced a user-facing change?

None

Issue fixed. Please take a look, thanks! /assign @xuliwenwenwen @harrisonliu5