Allow for separate string minimum size to store in binary store configuration

The minimum size for binary and string properties that are stored into the separate binary store can be configured using minimumBinarySizeInBytes. It would be useful as discussed in the forum reference to be able to configure the minimum size for BINARYs and STRINGs separately.

A new optional minimumStringSizeInBytes property should be provided in the binaryStorage configuration to allow a different setting for strings. If this property is not set it should default to the value of minimumBinarySizeInBytes to maintain existing behaviour.