Add the ability to use != approved-by in merge request filter

Related to #218570 (closed)

What does this MR do?

We are adding the ability for users to search by approved-by != USER in the merge request filter list

Here is query for only Approved-by != User query

https://explain.depesz.com/s/Scto

Query:

SELECT
    merge_requests.*
FROM
    merge_requests
WHERE
    merge_requests.target_project_id = 278964
    AND (merge_requests.state_id IN (1))
    AND NOT (EXISTS (
            SELECT
                TRUE
            FROM
                approvals
            WHERE
                approvals.user_id IN (
                    SELECT
                        users.id
                    FROM
                        users
                    WHERE
                        users.username = 'mshaw')
                    AND approvals.merge_request_id = merge_requests.id))
    ORDER BY
        merge_requests.created_at DESC,
        merge_requests.id DESC
    LIMIT 20 OFFSET 0

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