Add documentation for the 6.12 kernel in FIPS variants

[ginglis13]

Once the 6.12 kernel is released with support for FIPS and lands in variants, update https://bottlerocket.dev/en/os/1.44.x/version-information/fips-modules/

Track

• kernel-6.12: enable FIPS support bottlerocket-kernel-kit#263
• kernel-kit release
• bottlerocket release