Allow virtqemud domain transition to nbdkit

The commit addresses the following AVC denial:
type=PROCTITLE msg=audit(11/27/2024 02:11:06.515:615) : proctitle=/usr/sbin/virtqemud --timeout 120
type=PATH msg=audit(11/27/2024 02:11:06.515:615) : item=0 name=/usr/sbin/nbdkit inode=12677518 dev=fd:02 mode=file,755 ouid=root ogid=root rdev=00:00 obj=system_u:object_r:nbdkit_exec_t:s0 nametype=NORMAL cap_fp=none cap_fi=none cap_fe=0 cap_fver=0 cap_frootid=0
type=SYSCALL msg=audit(11/27/2024 02:11:06.515:615) : arch=x86_64 syscall=access success=yes exit=0 a0=0x7f79c80aa928 a1=X_OK a2=0x9 a3=0x0 items=1 ppid=1 pid=6131 auid=unset uid=root gid=root euid=root suid=root fsuid=root egid=root sgid=root fsgid=root tty=(none) ses=unset comm=rpc-virtqemud exe=/usr/sbin/virtqemud subj=system_u:system_r:virtqemud_t:s0 key=(null)
type=AVC msg=audit(11/27/2024 02:11:06.515:615) : avc:  denied  { execute } for  pid=6131 comm=rpc-virtqemud name=nbdkit dev="vda2" ino=12677518 scontext=system_u:system_r:virtqemud_t:s0 tcontext=system_u:object_r:nbdkit_exec_t:s0 tclass=file permissive=1

Resolves: RHEL-69118

policy/modules/contrib/virt.te

@@ -2285,6 +2285,10 @@ optional_policy(`
 	dnsmasq_filetrans_named_content_fromdir(virtqemud_t, virtqemud_var_run_t)
 ')
 
+optional_policy(`
+	nbdkit_domtrans(virtqemud_t)
+')
+
 optional_policy(`
 	numad_domtrans(virtqemud_t)
 ')