Add positive versions of rate and delta

[alejandrodnm]

Description of the changes

This PR adds unsigned versions of RATE and DELTA, this is driven by the fact that we had a check for non-negative RATE/DELTA then remove it, and now it's being asked again. This adds the flexibility to use both cases.

https://github.com/newrelic/infra-integrations-sdk/pull/110

PR Review Checklist

Author

• [x ] add a risk label after carefully considering the "blast radius" of your changes
• [x ] describe the intent of your changes in the description. don't just rewrite your code in prose
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Reviewer

• [ ] review code for readability
• [ ] verify that high risk behavior changes are well tested
• [ ] check license for any new external dependency
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