Search: Always show scope tabs regardless of tab selected

What does this MR do?

Related to #326470 (closed)

The Elasticsearch tabs (comments, code, commits, wiki) were only being shown if Elasticsearch is enabled for the search level (project, group, global) and if the selected tab was available in Elasticsearch. Currently if you move from a tab that is available in Elasticsearch (code) to a tab that isn't available (users), the Elasticsearch tabs would disappear.

This MR adds a new method to check whether the Elasticsearch tabs should be shown or not that only relies upon whether Elasticsearch is enabled for the search level (global, group, project). A new method was created because the original method was used for other things (such as showing whether Advanced Search was enabled in the UI).

Note: this only affects Group/Global search as the project search uses different logic for displaying tabs

Screenshots (strongly suggested)

Group - code search

Group - epics search

Group - users search

Global - users search

Does this MR meet the acceptance criteria?

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