fix(bootstrap): restore TPM FDE messaging

[d-loose]

@anasereijo this restores the message as a subtitle and looks the same as in 23.10. We can iterate on the design later if you have suggestions for improvements.

Fix #743 UDENG-2941

[anasereijo]

@d-loose Nitpicking, but if not too much work, could you disable the 'Experimental' label? Thank you!