Add ENV for ignoring transactions

[daveisfera]

Summary

Node and Ruby agents provide an ENV that is a regex for indicating which transactions should be ignored. This is requesting that the same be done for the Python agent because the current method requires controlling that in code which is a pain and inflexible.

Desired Behavior

Ability to specify a regex to ignore transactions

Possible Solution

Regex like the Node and Ruby agents support

[Newrelic-Boomi]

https://new-relic.atlassian.net/browse/NR-492015