Collect WebLogic specific attributes

[agoallikmaa]

This adds collection of WebLogic-specific attributes to servlet spans, and also provides middleware name and version through MiddlewareHolder.

Sample output from the logging collector:

Attributes:
     -> middleware.name: STRING(WebLogic Server)
     -> middleware.version: STRING(12.2.1.4.0)
     -> middleware.weblogic.server: STRING(admin-server)
     -> middleware.weblogic.application: STRING(weblogic)
     -> middleware.weblogic.domain: STRING(domain1)

No spans are created at WebLogic instrumentation level (no custom logic required), so this adds an instrumentation that only collects the attribute values, stores them as a map into otel.middleware ServletRequest attribute. The map contents are copied over to the span in another instrumentation where the servlet span is currently active.

WebLogic classes are not published as a public dependency, therefore its classes are accessed with Class.forName and MethodHandle instead of compiling against its classes directly. These are resolved by WebLogicEntity during its static initialization, which also provides wrapper classes for WebLogic classes. As an optimization, the full set of attributes is not collected on every request, but they are cached to a servlet context attribute.

[vovencij]

You can replace this FIXME with just a comment, that there aren't any server handlers for weblogic because of APMI-1300.

[mateuszrzeszutek]

Just wondering: have you considered adding a field to MiddlewareHolder and storing those attributes there instead of the request?

[sedmelluq]

The server and application fields may have different values in a single JVM, so the current static field approach MiddlewareHolder would not work there.