Use Ubuntu-specific Google API keys

[Jeremy Bícha]

Test Case
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In the "Welcome to Ubuntu" wizard in Ubuntu 18.10, on the Online Accounts Screen, click Google.
The dialog currently reads "Sign in to continue to GNOME"
After authenticating, it says "GNOME wants to access your Google account"

(Because it's a web page, Google can change the exact wording at any time.)

Suggestion
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Canonical should consider using its own Google API keys. I suggest using different keys at least for each LTS release.

Benefits
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These API keys have usage limits. Ubuntu is a substantial part of GNOME's usage and it makes sense to spread out the load more.

Occasionally, there is a need to replace keys. If Canonical already has a system for these keys, it might be able to replace these keys faster. An example of when it was needed was with Evolution 3.20 which had a bug (sort of a DDoS) that led to Google throttling all users of that API key.

Other Info
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Both GOA and EDS have Google keys and Canonical should probably use separate keys for each. (Users of the Evolution app can choose to use GNOME Online Accounts or authenticate directly in Evolution without using GOA.)