Audit and update buttons on SearchController#show

What does this MR do?

• Updates the Search button to use the confirm variant to align with button documentation in Pajamas.
• Updates the Apply button to use the confirm variant and small size.

An example page can be seen here https://gitlab.com/search?utf8=%E2%9C%93&search=test&group_id=&project_id=&snippets=false&repository_ref=&nav_source=navbar.

Screenshots

Before	After

Does this MR meet the acceptance criteria?

Conformity

• 📋 Does this MR need a changelog?
  • I have included a changelog entry.
  • I have not included a changelog entry because _____.
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

N/A

Security

N/A

Related to #273311 (closed)