release: Standardize on *-${FS}.* VM image naming

We publish three sets of VM images on download.freebsd.org:

• Generic VM images
• BASIC-CLOUDINIT VM images
• BASIC-CI VM images

Of these, the first had names like

FreeBSD-14.2-RELEASE-amd64-ufs.raw.xz,

the second had names like

FreeBSD-14.2-RELEASE-amd64-BASIC-CLOUDINIT.ufs.qcow2.xz,

and the third had names like

FreeBSD-14.2-RELEASE-amd64-BASIC-CI.ufs.raw.xz

but were listed in the CHECKSUM files with names like

FreeBSD-14.2-RELEASE-amd64-BASIC-CI-ufs.raw.xz

Standardize these to consistently use a hyphen before the filesystem
type rather than a period.

Note: On FreeBSD 14 we ship images without the -${FS} component in
their names; these are hardlinks to the -ufs images for compatibility
purposes. On FreeBSD 13 we only have UFS images and don't include the
filesystem in the name.

MFC after: 1 week
Reported by: jmg
Sponsored by: Amazon

(cherry picked from commit 35623ccc375846648f4dcdfc47c7e84fc9db4852)