Allow setting parameters for Content Enrichers

By allowing Content Enrichers to have parameters we can change their behaviour without any code changes. This will also allow introducing configurable Content Enrichers that can be reused in different scenarios.

For example, this can be used by the Permissions content enricher to configure the list of permissions to check for:

<enricher name="permissions" class="org.nuxeo.ecm.automation.io.services.enricher.UserPermissionsContentEnricher">
      <category>permissions</category>
      <parameter name="permissions">Read,Write,Everything</parameter>
</enricher>