SAML reauth banner for issues and merge requests dashboard

What does this MR do and why?

SAML reauth banner for issues and merge requests dashboard

Displays a banner on the issues and merge requests dashboard when a user has one or more SAML groups that require SSO reauthentication. This change makes slight modifications to the exist Todo dashboard banner and makes it re-usable for both Issues and Merge Requests.

It's worth noting that the approach for issues and merge requests is a bit naive. I felt this was the best first iteration and we can always decide to make it more specific later. Unlike Todos, in the dashboard controller we use IssuesFinder and MergeRequestsFinder respectively. These finders only return objects for which the user has permission, including whether they have an expired SAML SSO session. I was left with a decision to either re-query for all issues a user might be assigned to, or naively look to see if a user had any SAML session that was expired. I chose the latter, feeling it was more performant and probably good enough for these purposes. As a result I also slightly modified the language of the banner to indicate items may be hidden. I think this situation is an improvement over what we have now - which is not showing users issues/MRs when their session is expired.

Resolves #414475 (closed)

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Screenshots or screen recordings

Screenshots are required for UI changes, and strongly recommended for all other merge requests.

Before	After

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.