Implement ISO8601 durations as addition for Offset Aliases
#### Code Sample, a copy-pastable example if possible

```
current     -> query_config["aggregation"] = "5min"
proposed -> query_config["aggregation"] = "PT5M"

resampled_dataframe = dataframe.resample(query_config["aggregation"], how = query_config["aggregation_type"], closed = query_config["closed"])
```

#### Problem description

https://en.wikipedia.org/wiki/ISO_8601#Durations

Current behavior uses non standardized markup for time duration, wich can cause errors and confusion. Implementing ISO8601 duration grantees standardized solution for time duration in PANDAS. It does not have to replace the current system rather extend it.


