bootloader-builder: change the builder branch and the container version

https://jira.wrs.com/browse/ELXRPRO-522

1. change the builder branch to elxr/aria.
2. change the container version to v1.2.

Test steps:

1. $ git clone --branch elxr/aria https://gitlab.com/elxr/tools/bootloader-builder.git
2. $ cd bootloader-builder/docker
3. $ sudo docker build -t bootloader-builder:v1.2 .
4. $ sudo docker run -it -v /buildarea1/mwan1-cn/bootloader-builder:/mnt bootloader-builder:v1.2 /bin/bash
5. imx-bootloader-builder -t iMX8M -b build-imx-bootloader -i imx8m-bootloader.bin
6. Burn bootloader to SD card
   $ sudo dd if=imx8m-bootloader.bin of=/dev/sdb bs=1k seek=33 conv=fsync,notrunc
7. Insert SD card to imx8mq-evk, power on imx8mq-evk and check bootloader version:
   U-Boot 2023.042023.04+elxr-6 (Dec 18 2024 - 10:24:12 +0000)
8. After system boot up and check basic information
   root@localhost:# dmesg | grep 'BUG'
   root@localhost:# uname -a
   Linux localhost 6.1.0-32-imx-arm64 #1 SMP eLxr 6.1.129-elxr2-1 (2025-04-23) aarch64 GNU/Linux
   root@localhost:~# lsblk
   NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINTS
   mtdblock0 31:0 0 32M 0 disk
   mmcblk0 179:0 0 14.7G 0 disk
   └─mmcblk0p1 179:1 0 14.7G 0 part
   mmcblk0boot0 179:256 0 4M 1 disk
   mmcblk0boot1 179:512 0 4M 1 disk
   mmcblk1 179:768 0 14.8G 0 disk
   ├─mmcblk1p1 179:769 0 112M 0 part /efi
   ├─mmcblk1p2 179:770 0 488M 0 part /boot
   └─mmcblk1p3 179:771 0 14.2G 0 part /var
   /
   /sysroot