Make search header message configurable

[Blake-]

The current header on the /search?reset=true search page wasn't easily customized. This changes that with a new locale and a change to the _search.html.erb file.

Motivation and Context

Trying to change "Search The Archives" was nearly impossible.

How Has This Been Tested?

Brought up build locally and tested. The message is unchanged from the original, but it is now easily changed via en.yml

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• [x ] New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• [x ] My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• [ x] I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• [x ] All new and existing tests passed.

[cdibella]

@Blake- Looks like a useful change to me - thanks for submitting it!