feat: add customization options for the login page (#5633)

* add customization options for the login page

* add unit tests

* add test for correct welcome text when none is set but app-name is

Signed-off-by: niwla23 <46248939+niwla23@users.noreply.github.com>

* add test for no app-name set and check in title too

Signed-off-by: niwla23 <46248939+niwla23@users.noreply.github.com>

Signed-off-by: niwla23 <46248939+niwla23@users.noreply.github.com>
Co-authored-by: Joe Previte <jjprevite@gmail.com>