PRIP API: Add "BooleanAttribute" as per PRIP ICD v1.5

[tangobravo62]

PRIP ICD v1.5 introduces a new attribute type "BooleanAttribute". This shall be implemented throughout the prosEO PRIP.

Note that the missions currently discussed for the use of prosEO do not make use of boolean attributes, therefore the urgency of this issue is low.

[tangobravo62]

Implemented as per the current PRIP metadata document:

<?xml version="1.0" encoding="UTF-8"?>
<edmx:Edmx Version="4.0" xmlns:edmx="http://docs.oasis-open.org/odata/ns/edmx">
    <edmx:DataServices>
        <Schema xmlns="http://docs.oasis-open.org/odata/ns/edm" Namespace="OData.CSC">
            [...]
            <EntityType Name="Product" HasStream="true">
                <Key>
                    <PropertyRef Name="Id"/>
                </Key>
                [...]
                <NavigationProperty Name="Attributes" Type="Collection(OData.CSC.Attribute)"></NavigationProperty>
                <NavigationProperty Name="StringAttributes" Type="Collection(OData.CSC.StringAttribute)"></NavigationProperty>
                <NavigationProperty Name="IntegerAttributes" Type="Collection(OData.CSC.IntegerAttribute)"></NavigationProperty>
                <NavigationProperty Name="DoubleAttributes" Type="Collection(OData.CSC.DoubleAttribute)"></NavigationProperty>
                <NavigationProperty Name="BooleanAttributes" Type="Collection(OData.CSC.BooleanAttribute)"></NavigationProperty>
                <NavigationProperty Name="DateTimeOffsetAttributes" Type="Collection(OData.CSC.DateTimeOffsetAttribute)"></NavigationProperty>
            </EntityType>
            [...]
        </Schema>
    </edmx:DataServices>
</edmx:Edmx>