Revert OTA hack

[gminn]

Summary

We had a hack to get OTA working that involved trying indefinitely
to get a successful firmware upgrade. Failures would happen in the
middle of pulling the payload, seemingly connected to a context switch
where another thread started interacting with the modem.

This problem was actually caused by a bug in our FOTA code, where
the dynamic memory holding the download URL would sometimes get
freed early. The latest SDK release fixed this bug, so we are pulling in
that fix and reverting the indefinite retrying logic.

Also, add a github action that builds the app. Long overdue!
With the memfault version bumped up, the build fails due to insufficient
space. We added the self test, which caused this image size bump of
about ~1kB. Disabling the memfault shell for now until we get the option
to disable the self test (currently a feature in review).

Test Plan

OTA fails when the hack is removed but before pulling in the SDK fix:

[00:01:57.313,293] <inf> download_client: Downloaded 260096/428252 bytes (60%)
[00:01:57.416,229] <inf> app_event_manager: DATA_EVT_DATA_READY
[00:01:57.433,746] <inf> app_event_manager: DATA_EVT_DATA_SEND_BATCH
[00:01:57.434,875] <inf> app_event_manager: CLOUD_EVT_DATA_SEND_QOS
[00:01:57.718,383] <inf> download_client: Downloaded 261120/428252 bytes (60%)
[00:01:57.952,270] <err> download_client: Unexpected HTTP response: 400 bad request
[00:01:57.952,301] <err> fota_download: Download client error
[00:01:57.952,301] <inf> dfu_target_mcuboot: MCUBoot image upgrade aborted.
[00:01:57.952,392] <inf> dfu_target_mcuboot: MCUBoot image upgrade aborted.

OTA succeeds after pulling in SDK fix. Notice no error when there is a context switch.

[00:01:57.195,983] <inf> download_client: Downloaded 267264/428252 bytes (62%)
[00:01:57.283,020] <inf> app_event_manager: DATA_EVT_DATA_READY
[00:01:57.314,147] <inf> app_event_manager: DATA_EVT_DATA_SEND_BATCH
[00:01:57.315,368] <inf> app_event_manager: CLOUD_EVT_DATA_SEND_QOS
[00:01:57.616,180] <inf> download_client: Downloaded 268288/428252 bytes (62%)
[00:01:57.938,964] <inf> download_client: Downloaded 269312/428252 bytes (62%)
[00:01:58.661,651] <inf> download_client: Downloaded 270336/428252 bytes (63%)

Github action testing:

• Failed before adding CONFIG_MEMFAULT_SHELL=n (see here)
• Succeeded (is one of the checks in this PR) after adding

---

Resolves: MFLT-12841

[noahp]

You served us well, workaround 🫡