Add influxdb retention policy

[DLeich]

Use Case

When collecting a lot of metrics for a scaled-out puppet environment with several compile masters, you can find yourself storing metrics for a longer time period than is necessary. Additionally, you can start to run out of disk space quite quickly. Adding an influxdb retention policy can help alleviate those issues.

Describe the Solution You Would Like

influxdb.conf can take a configuration value for a default retention policy on new db's.

Describe Alternatives You've Considered

For now, I have applied a retention policy manually to the telegraf db after it was created

Additional Context