PrefName: Fix capitalization of First Name in welcome message

[wesrowe]

Description

User story

As a Veteran, I don't want my first name in the welcome message on the MHV landing page to be displayed in all caps, so that I feel as welcome as intended.

Notes

• in demo on 12/17, Kaitlin did a live demo in prod and we saw that her first name on the landing page was all-caps.
• may be related to PrefName: Profile: Preserve/display user's capitalization #97412, which covers the same problem on the Personal Information page of Profile
• also, preferredName is still not preserving user's intended casing. some discovery happened in this slack thread, where it appears maybe casing is getting manipulated after preferredName is sent from the Profile page to vets-api.

Possible tasks:

Acceptance criteria

• 1. In case where a Veteran's data in VA.gov includes a first name but not a preferred name, the name capitalization in the landing page "Welcome" message matches the capitalization in the auth menu in the header.
• 2. Determined whether we have to do anything in vets-website or vets-api to preserve user's intended capitalization of preferredName, and ticketed if needed
• QA review