Added ostrom tariff

[kscholty]

In discussion https://github.com/evcc-io/evcc/discussions/15512 and closed issue https://github.com/evcc-io/evcc/issues/11148 people are asking for Ostrom support. Since they have a public API and I had some spare time I implemented a tariff for EVCC.

The implementation supports both the SIMPLY_FAIR (fixed price for at least a month) and the SIMPLY_DYNAMIC (hourly rates) tariff, which would make it worth having a native implementation. The prices for both tariffs are queried on a regular basis.

Client credentials can be created under https://developer.ostrom-api.io/

Looking forward to your comments