XSD-Schema: missing `minOccurs="0"` in element `value` of `file_t`

Class File has attribute value with cardinality 0..1:

Therefore, the XSD-Schema should have a minOccurs="0" in the element defintion of value to comply with this.

Current Version:

	<complexType name="file_t">
		<complexContent>
			<extension base="aas:submodelElementAbstract_t">
				<sequence>
					<element name="mimeType" type="string"/>
					<element name="value" type="aas:pathType_t"/>
				</sequence>
			</extension>
		</complexContent>
	</complexType>

Proposed Fix:

	<complexType name="file_t">
		<complexContent>
			<extension base="aas:submodelElementAbstract_t">
				<sequence>
					<element name="mimeType" type="string"/>
					<element minOccurs="0" name="value" type="aas:pathType_t"/>
				</sequence>
			</extension>
		</complexContent>
	</complexType>