[BUG] Warning Application Not Found is shown when trying to access to 'Dashboards' if no index pattern exists and it's in readonly mode

[machenity]

Describe the bug

When

• there's no index pattern registered in the OpenSearch Dashboards and
• there's a user with a role that is configured as opensearch_security.readonly_mode.roles,

A warning Application Not Found is shown when the user is trying to access to Dashboards.

I guess that original behavior when there's no index pattern is redirection to Dashboard Management UI but it might not be shown in readonly mode.

To Reproduce
Steps to reproduce the behavior:

1. Configure opensearch_security.readonly_mode.roles in opensearch_dashboards.yml
2. Prepare a user with a role that is configured in 1.
3. Ensure there is no index pattern registered in the dashboards.
4. Access to OpenSearch Dashboards > Dashboards
5. See error

Expected behavior
Show more precise, kind error explanation of the situation.

OpenSearch Version
2.18.0

Dashboards Version
2.18.0

Screenshots

Host/Environment (please complete the following information):

• OS: macOS
• Browser and version: chromium