Update alert thresholds for mainnet and devnet

[amc-mina]

[amc-ie]

The CriticallyLowMinWindowDensity alert threshold needs to be changed on mainnet, at present it is not the correct value and is causing a lot of alerts to be triggered.

We also need to split this out as an additional alert for devnet so we can leave the threshold for that "as is".

See here for additional information.