Improve wording for date picker instructions

[finekatie]

Summary

Given the hint text update we added in uswds/uswds#6147, how do we feel about the hint text guidance we're suggesting in #2822?

"Provide a hint of mm/dd/yyyy to help users enter the proper date format if they opt not to use the date picker."

We should review and take another pass.

Related to: #6186 and #6061.

Other related info:
Time picker instructions are being updated in uswds/uswds#6147 , but we might want to look into how to improve in future.

From @annepetersen : The tiny phrasing improvement we could make in the future might be figuring out a better word than "input," which might be jargon-y for some people. Also noting "input" wasn't in the uswds/uswds#6061 (comment).

[finekatie]

Added per Slack discussion 11/6. https://gsa-tts.slack.com/archives/C050HRGN7/p1730933647401159