[Search] Update search bar layout

[plutonik-a]

Delete current placeholder, add https://standards.usa.gov/components/search-bar/ styling with a search icon.

Parent: #284
Related: #294

[joewiz]

Please replace the magnifying glass icon with "Search" in the keyword search input field, as this instance appears to fall into the "medium" or "large" category in the https://standards.usa.gov/components/search-bar/ guidelines.

[plutonik-a]

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