no deb package in ARM64

filebeat community provide arm64 deb package from 7.12.

set install_sources to "deb https://artifacts.elastic.co/packages/6.7/apt stable main" might work

Start by checking how the filebeat charm handles the install_sources setting and whether the referenced apt source provides an ARM64 deb package. The issue names no file or test, so confirm the expected ARM64 installation path before determining what should count as done.

Written by the indexing model from the issue text.