Verbose warning message for PRODUCT_INSTALL_DEBUG_POLICY_TO_SYSTEM_EXT

I56ed328a9ae70cf49dbd3c6efb5a4a8c54e1b7a7 added a validation check to
otatools to check the target_files archive for the existence of
userdebug_plat_sepolicy.cil. That check superseded the original
PRODUCT_INSTALL_DEBUG_POLICY_TO_SYSTEM_EXT product_config.mk check and
is more robust because it can handle not only phone GSI but also car/tv
GSI (downstream of phone GSI).

Modify the check to show a scary wall of text if non-compliance-GSI
products tried to set PRODUCT_INSTALL_DEBUG_POLICY_TO_SYSTEM_EXT,
instead of erroring out immediately.
Also add gsi_car_arm64 & gsi_car_x86_64 to the list of eligible GSI
product names.

After this change, any product can set
PRODUCT_INSTALL_DEBUG_POLICY_TO_SYSTEM_EXT for development purposes, but
only GSI products that specifies `--allow_gsi_debug_sepolicy` during
image signing can release sign a product built with
PRODUCT_INSTALL_DEBUG_POLICY_TO_SYSTEM_EXT.

Bug: 188067818
Test: Presubmit
Test: lunch gsi_arm64-userdebug && m nothing  # => no warning
Change-Id: I34ef49af29c7064bea8924b0070793f1e78256bf