Set default query string when searching with filters

What does this MR do?

This MR is to set the default query string to a wildcard when using filters.

For details about Advanced Search syntax, please refer to https://docs.gitlab.com/ee/user/search/advanced_search_syntax.html#syntax-search-filters

Follow-up: Normally, we should include the doc updates with the code change. For this one, it's Advanced Searech Syntax. However, it would be nice we can include the usage examples in the document. So, I need to wait until this MR lands on production in order to include a real example in the documentation.

Screenshots (strongly suggested)

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team