[CrOS Cellular] Update add eSIM dialog next button

Updates the "forward" button in the add eSIM dialog, to reflect the
correct state of profile selection. In the profile discovery page
when a profile is selected by default the forward button text should
indicate the profile can be installed. This change makes sure of that.

Fixed: b/331795705
Test: Deployed to DUT and updated unittest
Change-Id: Ie30b1604a8b7cf01b6d33c5eb2c771b1d59c0933
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5406686


Commit-Queue: Theo Johnson-kanu <tjohnsonkanu@google.com>
Reviewed-by: Chad Duffin <chadduffin@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1280309}