Update docs to cover how resources and test steps interact with Open() and Close() methods

At a minimum update https://gitlab.com/OpenTAP/opentap/-/blob/master/sdk/Examples/PluginDevelopment/TestSteps/Attributes/AvailableValuesAttributeExample.cs to use [ResourceOpen(ResourceOpenBehavior.Ignore)]

• Add information about the attribute to the dev guide.
• Add information about how resources are located and opened/closed in the developer guide.
• Add information about lazy/eager resource management.