Faster Advanced Searching update

What does this MR do?

Rewrites this statement to provide less ambiguity.

If you are dealing with huge amount of data and want to keep GitLab's search
fast, Advanced Search will help you achieve that.

Removes this older note, to provide less version-specific messaging.

NOTE:
Between versions 12.10 and 13.4, Advanced Search response times have improved by 80%.

This will be referenced in the 13.7 Release Post. 

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