Add an argument `boot-uuid` to bootupctl install

With https://github.com/bootc-dev/bootc/pull/1816, bootc install on existing FCOS test failed.

When running bootc install without separate /boot, if chroot to the ostree deployment, the write_uuid will fail as inspected the / filesystem as it is not mounted.

Copy failed log from https://github.com/bootc-dev/bootc/actions/runs/20912844659/job/60080780702?pr=1816

                        content: Installed: grub.cfg
                        content: error: boot data installation failed: Installing static GRUB configs: Inspecting filesystem ".": Subprocess failed: ExitStatus(unix_wait_status(256))
                        content: 
                        content: error: Installing to filesystem: Installing bootloader: Failed to run command: Command {
                        content:     program: "chroot",
                        content:     args: [
                        content:         "chroot",
                        content:         "/target/ostree/deploy/default/deploy/e1522e8dbaa55a684e1906a1ef7e91ea7f3014db86c25f84e3ab31be356eb247.0",
                        content:         "bootupctl",
                        content:         "backend",
                        content:         "install",
                        content:         "--write-uuid",
                        content:         "--update-firmware",
                        content:         "--auto",
                        content:         "--device",
                        content:         "/dev/vda",
                        content:         "/",
                        content:     ],
                        content:     env: CommandEnv {
                        content:         clear: false,
                        content:         vars: {
                        content:             "PATH": Some(
                        content:                 "/bin:/usr/bin:/sbin:/usr/sbin:/usr/local/bin:/usr/local/sbin",
                        content:             ),
                        content:         },
                        content:     },
                        content:     create_pidfd: false,
                        content: }

To workaround, one option is pass boot-uuid to bootupctl as it already detect in bootc (https://github.com/bootc-dev/bootc/blob/main/crates/lib/src/install.rs#L1568)

Start with the bootc install logic referenced at crates/lib/src/install.rs:1568 and trace how bootupctl backend install receives boot information. Reproduce the failing existing-FCOS case from the linked log, then verify that bootupctl install accepts boot-uuid and that the installation no longer fails when /boot is not separate.