Feature request: "interval start" field support in CSV rate importer

[nitefood]

Description

When importing rates manually into IvozProvider, you can specify the useful interval start field. The same field is not present in the automated CSV importer. It would be very useful to be able to import it in order to adapt carrier rates for particular destinations with atypical billing schemes.

Thanks!

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• I'm willing to:

• [ ] Implement this feature myself

• [ ] Pay to priorize this new feature

Additional Information

To make an example of the usefulness of this field, based on one of my real life use cases, I have some carriers billing me with 60/1 billing schemes for certain prefixes, where the call is billed for a whole minute on connection, and then the billing proceeds per-second after the first minute. This can be easily adapted into Ivoz logic thanks to the interval start field (ie you set connection fee to the per-minute cost, interval start to 60s, and charge period to 1s - so that the first minute is billed on connection, then the rating engine considers it "free" for 60s, and then billing continues per-second after the first minute).