Increase cells in London from 9 to 11
Increase cells in London from 9 to 11

The "DiegoCellRepMemoryCapacity_Critical" is currently firing in
prod-lon, because `rep_memory_capacity_pct:avg5m` is sitting around
30.8%, which is less than the threshold of 33.

Increasing the number of instances to 10 would probably only increase
the free memory by 1/9, which would only just put us above the threshold
of 33:

30.8 + 30.8 * 1/9 = 34.2%

Scaling up to 11 should increase the free memory by 2/9, which gives us
a bit more margin:

30.8 + 30.8 * 2/9 = 37.6%

The numbers may not work out quite so neatly in reality, so we'll have
to keep an eye on the metrics.

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