Sort by similarity in Search Group dropdown [RUN ALL RSPEC] [RUN AS-IF-FOSS]

What does this MR do?

Related to #332889 (closed)

Update the Search page Group dropdown to send an order_by param set to similarity. The similarity option was introduced in: !63674 (merged)

Add a new test

How to test

• Navigate to the search page: http://gdk.test:3000/search
• search in the Group dropdown

you can verify the SQL by using the performance bar that it is using similarity in the order by clause

Screenshots (strongly suggested)

Taken from my gdk where I staged some group names to match what we see on GitLab.com

Before

After

Does this MR meet the acceptance criteria?

Conformity

• I have included changelog trailers, or none are needed. (Does this MR need a changelog?)
• I have added/updated documentation, or it's not needed. (Is documentation required?)
• I have properly separated EE content from FOSS, or this MR is FOSS only. (Where should EE code go?)
• I have added information for database reviewers in the MR description, or it's not needed. (Does this MR have database related changes?)
• I have self-reviewed this MR per code review guidelines.
• This MR does not harm performance, or I have asked a reviewer to help assess the performance impact. (Merge request performance guidelines)
• I have followed the style guides.
• This change is backwards compatible across updates, or this does not apply.

Availability and Testing

• I have added/updated tests following the Testing Guide, or it's not needed. (Consider all test levels. See the Test Planning Process.)
• I have tested this MR in all supported browsers, or it's not needed.
• I have informed the Infrastructure department of a default or new setting change per definition of done, or it's not needed.

Security

Does this MR contain changes to processing or storing of credentials or tokens, authorization and authentication methods or other items described in the security review guidelines? If not, then delete this Security section.

• 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