require confirm for flash initialization

[tehn]

What does this PR do?

on flash_reset detection (checking magic number in flash_prepare) blink a light and wait for confirmation by pressing key down. otherwise it times out and doesn't run.

Provide links to any related discussion on lines.

How should this be manually tested?

works perfectly well for newly flashed units. we'd need to see the bug-state to trigger this, which isn't known. it's a protection measure at this point.

Any background context you want to provide?

If the related Github issues aren't referenced in your commits, please link to them here.

I have,

• updated CHANGELOG.md
• updated the documentation
• run make format on each commit

[tehn]

note

this is a confusing mechanism, to protect flash.

if you're flashing "fresh" from git you must hit the button within the flashing-period, otherwise boot will fail (haven't had a minute to understand why)

if you're flashing from a hex file with presets the magic number will already be set and you won't be presented with the flashing-need-for-pressing-button