Add implementation to build user schema extension with InputStream

[senthuran16]

Purpose

Currently, we only have the following method, where configFilePath is the path of SCIM2 Schema Extension config file (eg: scim2-schema-extension.config).

SCIMUserSchemaExtensionBuilder.getInstance().buildUserSchemaExtension(configFilePath)

In IS7 Connector [1], we pack this SCIM2 Schema Extension config file as a resource. For a resource file, we can get an InputStream, and it won't be possible to treat it as a file and get a file path. Therefore, we need to be able to build user schema extension with this InputStream as:

InputStream schemaExtensionConfigInputStream = ClaimMappingReader.class.getClassLoader()
                    .getResourceAsStream(SCIM2_SCHEMA_EXTENSION_CONFIG_FILE);
SCIMUserSchemaExtensionBuilder.getInstance().buildUserSchemaExtension(schemaExtensionConfigInputStream);

This PR introduces the buildUserSchemaExtension(InputStream inputStream) method. Fixes wso2/api-manager#2693

[1] wso2-extensions/apim-km-wso2is#135