Allow access to schemas in nested JARs

[qligier]

Hello! While migration an application to IPF 6.0.0, I encountered a new bug preventing the load of some schemas.
My app is packaged as a fat JAR by spring-boot-maven-plugin, which means the schema URLs look like jar:nested:/myapp.jar/!BOOT-INF/lib/ipf.jar!/schema/x.xsd. The current LOCAL_ACCESS_ONLY prevents such URLs using nested from being accessed, since it only allows jar and file.

Example error stack trace:

org.openehealth.ipf.commons.core.modules.api.ValidationException: Unexpected validation failure because Could not initialize XSD schema
Could not initialize XSD schema
        at org.openehealth.ipf.commons.xml.XsdValidator.validate(XsdValidator.java:67) ~[ipf-commons-xml-6.0.0.jar!/:6.0.0]
        at org.openehealth.ipf.commons.xml.CombinedXmlValidator.validate(CombinedXmlValidator.java:47) ~[ipf-commons-xml-6.0.0.jar!/:6.0.0]
        ... 23 common frames omitted
Caused by: org.openehealth.ipf.commons.core.modules.api.ValidationException: Unexpected validation failure because Could not initialize XSD schema
Could not initialize XSD schema
        at org.openehealth.ipf.commons.xml.XsdValidator.doValidate(XsdValidator.java:100) ~[ipf-commons-xml-6.0.0.jar!/:6.0.0]
        at org.openehealth.ipf.commons.xml.XsdValidator.validate(XsdValidator.java:65) ~[ipf-commons-xml-6.0.0.jar!/:6.0.0]
        ... 33 common frames omitted
Caused by: java.lang.IllegalArgumentException: Could not initialize XSD schema
        at org.openehealth.ipf.commons.xml.XsdValidator.createResource(XsdValidator.java:116) ~[ipf-commons-xml-6.0.0.jar!/:6.0.0]
        at org.openehealth.ipf.commons.xml.XsdValidator.createResource(XsdValidator.java:42) ~[ipf-commons-xml-6.0.0.jar!/:6.0.0]
        at org.openehealth.ipf.commons.xml.AbstractCachingXmlProcessor$1.load(AbstractCachingXmlProcessor.java:144) ~[ipf-commons-xml-6.0.0.jar!/:6.0.0]
        at org.openehealth.ipf.commons.xml.AbstractCachingXmlProcessor$Loader.get(AbstractCachingXmlProcessor.java:59) ~[ipf-commons-xml-6.0.0.jar!/:6.0.0]
        at org.openehealth.ipf.commons.xml.AbstractCachingXmlProcessor.resource(AbstractCachingXmlProcessor.java:147) ~[ipf-commons-xml-6.0.0.jar!/:6.0.0]
        at org.openehealth.ipf.commons.xml.XsdValidator.doValidate(XsdValidator.java:81) ~[ipf-commons-xml-6.0.0.jar!/:6.0.0]
        ... 34 common frames omitted
Caused by: org.xml.sax.SAXParseException; systemId: jar:nested:/D:/my-app/target/my-app-1.jar/!BOOT-INF/classes/!/schema/sts.xsd; lineNumber: 7; columnNumber: 116; schema_reference: Failed to read schema document 'ihe-appc-xacml-hl7-datatypes-base-1.0-epr-20211018.xsd', because 'nested' access is not allowed due to restriction set by the accessExternalSchema property.
        at java.xml/com.sun.org.apache.xerces.internal.util.ErrorHandlerWrapper.createSAXParseException(ErrorHandlerWrapper.java:204) ~[na:na]
        at java.xml/com.sun.org.apache.xerces.internal.util.ErrorHandlerWrapper.fatalError(ErrorHandlerWrapper.java:178) ~[na:na]
        at java.xml/com.sun.org.apache.xerces.internal.impl.XMLErrorReporter.reportError(XMLErrorReporter.java:400) ~[na:na]
        at java.xml/com.sun.org.apache.xerces.internal.impl.xs.traversers.XSDHandler.reportSchemaErr(XSDHandler.java:4256) ~[na:na]
        at java.xml/com.sun.org.apache.xerces.internal.impl.xs.traversers.XSDHandler.reportSchemaFatalError(XSDHandler.java:4235) ~[na:na]
        at java.xml/com.sun.org.apache.xerces.internal.impl.xs.traversers.XSDHandler.getSchemaDocument(XSDHandler.java:2221) ~[na:na]
        at java.xml/com.sun.org.apache.xerces.internal.impl.xs.traversers.XSDHandler.resolveSchema(XSDHandler.java:2130) ~[na:na]
        at java.xml/com.sun.org.apache.xerces.internal.impl.xs.traversers.XSDHandler.constructTrees(XSDHandler.java:1051) ~[na:na]
        at java.xml/com.sun.org.apache.xerces.internal.impl.xs.traversers.XSDHandler.parseSchema(XSDHandler.java:653) ~[na:na]
        at java.xml/com.sun.org.apache.xerces.internal.impl.xs.XMLSchemaLoader.loadSchema(XMLSchemaLoader.java:618) ~[na:na]
        at java.xml/com.sun.org.apache.xerces.internal.impl.xs.XMLSchemaLoader.loadGrammar(XMLSchemaLoader.java:577) ~[na:na]
        at java.xml/com.sun.org.apache.xerces.internal.impl.xs.XMLSchemaLoader.loadGrammar(XMLSchemaLoader.java:543) ~[na:na]
        at java.xml/com.sun.org.apache.xerces.internal.jaxp.validation.XMLSchemaFactory.newSchema(XMLSchemaFactory.java:279) ~[na:na]
        at java.xml/javax.xml.validation.SchemaFactory.newSchema(SchemaFactory.java:613) ~[na:na]
        at org.openehealth.ipf.commons.xml.XsdValidator.createResource(XsdValidator.java:114) ~[ipf-commons-xml-6.0.0.jar!/:6.0.0]
        ... 39 common frames omitted