We don’t have any way of playing back the totals we send to performance
platform.
This commit copies the command used to backfill the processing time and
adapts it to backfill the totals instead. Under the hood it uses the
same code that we use in the scheduled tasks to update performance
platform on a daily basis. I had to modify this code to take a `day`
argument because it was hardcoded to only work for ‘yesterday’.
(saves us having to write the stuff ourselves). Also adds a small
click plugin to do datetime parsing.
Sample output:
```
[leohemsted:~/dev/api]$ flask command create_provider_rates --help
Usage: flask command create_provider_rates [OPTIONS]
Backfill rates for a given provider
Options:
-p, --provider_name [mmg|firetext|ses]
[required]
-c, --cost FLOAT Cost (pence) per message including decimals
[required]
-d, --valid_from DATE [required]
--help Show this message and exit.
[leohemsted:~/dev/api]$ flask command create_provider_rates -p ses -c 1.234 -d invalid
Usage: flask command create_provider_rates [OPTIONS]
Error: Invalid value for "-d" / "--valid_from": Could not parse datetime string "invalid" formatted as %Y-%m-%dT%H:%M:%S
```
