improve email content of common bots

Id like to see several things:

- As part of the title an indication of whether this is staging (Koran) or production (xdai), i.e. `[Staging] failed to update ...`
- Now it says "failed to update common", can it be "failed to update proposal" (if you call "update-proposal-by-id")
- Include the response of the failing call as well (some of these errors are transient, and so we cannot reproduce why it failed)

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