profcollectd: OTA Observer

Pack any existing ETM profiles when an OTA is ready to install,
which simplifies the workflow for reporting profcollectd profiles.

Future work will use the same observer to upload profiles to a
collection service.

Bug: 79161490
Test: vendor/google/tools/fake-ota streaming on
Change-Id: I106af19a3360b87d19ceafaa3ef3b97f1cf34244