Ensure defaultSentryDSN is set in the Firefox tree

[ianb]

My simple attempt to import Screenshots into the tree left browser/extensions/screenshots/webextension/build/buildSettings.js with an empty DSN.

[ianb]

This is set by the environmental variable $SCREENSHOTS_SENTRY which should set before building. The value for prod is https://d58fc53f92cd47bba7266ad6444514d8@sentry.prod.mozaws.net/74

So this should do it:

$ SCREENSHOTS_SENTRY="https://d58fc53f92cd47bba7266ad6444514d8@sentry.prod.mozaws.net/74" ./bin/export_mc.py ...

However, it looks like export_mc.py has some server settings, it would be great to include these Sentry settings too. So the settings should be:

DEFAULT_SENTRY = {
    "local": "",
    "dev": "https://d58fc53f92cd47bba7266ad6444514d8@sentry.prod.mozaws.net/74",
    "stage": "https://3d2efd7bad9e4e359014cb4e69b8eaec@sentry.prod.mozaws.net/140",
    "prod": "https://97d8afa496f94764ae255e739b147f4b@sentry.prod.mozaws.net/139",
}