[FEATURE REQUEST]: Support System.Decimal in CreateDataFrame API

**Is your feature request related to a problem? Please describe.**
I'd like to be able to use the `System.Decimal` type when using the CreateDataFrame API. Currently when running the following:

```
decimal? minValue = 4.0M;
decimal? maxValue = 5.0M;
var df = sparkSession.CreateDataFrame(
new List
{
new GenericRow(
new object[]
{
"1234",
minValue,
maxValue,
}),
},
new StructType(
new List()
{
new StructField("id", new StringType()),
new StructField("minValue", new DecimalType()),
new StructField("maxValue", new DecimalType()),
}));
df.Show();
```

We see the following error:
`System.NotSupportedException: 'Type System.Decimal not supported yet'`

This presents issues in trying to unit test code that reads decimal types from a DB.

**Describe the solution you'd like**
To be able to create Dataframes with Decimals without an error 😄

**Describe alternatives you've considered**
Alternatives for us might be to change the type being read from the DB, but this is a significant challenge - for now we are unable to unit test this code.

**Additional context**
N/A