Add placeholder text for docs search input

[codedbychavez]

Description

Add a custom placeholder text to the search input. Additionally, this change matches the page title of the /search page for consistency.

Before:

After:

Notes for QA

What part of the application were affected by the changes?

• The search input placeholder text for the search popup.

What should be tested?

• Check if the new placeholder is ok.

Requirement checklist

• I have validated my changes on a test/local environment.
• I have tested that the code snippets I added work. (Leave unchecked if there are no new code snippets.)
• I have added my changes to the V1 and V2 documentations.

[codedbychavez]

Closing this PR as we haven't yet decided on making this change.