Adjust git push targets and thresholds after review

Closes #408 (closed)

After evaluating our real customer data points it's likely we're currently overtesting Git Push endpoints. A recent 50k customer reported around 15k pushes per hour, we're currently testing Git Push at magnitudes much higher in line with other Git endpoints - currently 360k.

With the above data and the adage of making sure we're testing with ample headroom (double and then double again) I'm going to propose we reduce the Git Push target from 10% of the API target down to 2% (72k requests per hour on 50k). We're still testing here with substantial head room but at a more realistic number.