local_manifests: Add GS290 to a15

<?xml version="1.0" encoding="UTF-8"?>

<manifest>

  <project name="e/devices/device_gigaset_gs290" path="device/gigaset/GS290" remote="e"/>

  <project name="e/devices/kernel_gigaset_gs290" path="kernel/gigaset/GS290" remote="e"/>

  <project name="e/devices/android_device_mediatek_sepolicy-vndr" path="device/mediatek/sepolicy_vndr" remote="e"/>

  <project name="e/devices/android_hardware_mediatek" path="hardware/mediatek" remote="e" />

</manifest>