site-config: Reduce auth session duration
Created by: miveronese
Jira ticket: CLOUD-247
This PR reduces the session length from 90 days to 7 days as recommended in the ticket linked above
Blocked by this PR: https://github.com/sourcegraph/clabot-config/pull/51
Test plan
- All existing tests should pass.
- When adding the configuration for "auth.sessionExpiry" (under User Admin > Site Configuration), the user should see an updated description for that field (informing that the default value is 7 days).