install_arch: align partition end, update root partition type, partition labels and ESP volume label

install_arch: align partition end

sgdisk does not align the partition size/end by default. The -I/--align-end option needs to be used to enable alignment. See https://wiki.archlinux.org/title/Advanced_Format#Partition_alignment

Additionally use the partition names (PARTLABELs) that gdisk and cgdisk set (but sgdisk doesn't) and follow the Discoverable Partitions Specification by useing the appropriate partition for the root partition. See https://wiki.archlinux.org/title/Partitioning#Single_root_partition

install_arch: improve the ESP file system label

Use an uppercase LABEL to avoid a warning from mkfs.fat:

mkfs.fat: Warning: lowercase labels might not work properly on some systems

Use something other than "efi" as the label since some firmware do not like it. While this is not really an issue for Arch infrastructure, since there is zero change that this will be run on any MSI hardware with its broken firmware, it is best to simply folow the wiki anyway. See https://wiki.archlinux.org/title/EFI_system_partition#Firmware_does_not_see_the_EFI_directory

install_arch: create all partitions with a single sgdisk command

There is no need to split up partitioning into per-partition tasks.