Add middleware to process semantic conventions

As discovered while analyzing the request from #1143, it became apparent that the current semantic conventions do lack the information about the middleware running on the runtime within the process. Adding this information makes the traces more valuable - the proposed change makes it possible to visualize that Tomcat 9.0.39 application server is sending messages to a Kafka message queue which in turn has a subscriber running on GlassFish 5.0 persisting the content to Druid 0.15.0. In the current form, it seems that the semantic conventions leave this information at the span level, which would be creating redundancy in outbound communication from the agent and/or not capture the information in unified manner, making it harder for Otel-compliant servers to visualize such traces.

specification/resource/semantic_conventions/process.md

@@ -131,3 +131,59 @@ Examples for some Ruby runtimes
 | --- | --- | --- | --- |
 | MRI | ruby | 2.7.1 | ruby 2.7.1p83 (2020-03-31 revision a0c7c23c9c) [x86_64-darwin19] |
 | TruffleRuby | truffleruby | 2.6.2 | truffleruby (Shopify) 20.0.0-dev-92ed3059, like ruby 2.6.2, GraalVM CE Native [x86_64-darwin] |
+
+## Process middlewares
+
+**type:** `process.middleware`
+
+**Description:** The single middleware instance which is monitored on the runtime in this process.
+
+| Attribute  | Description  | Example  | Required |
+|---|---|---|--|
+| process.middleware.type | Standardized attribute, specifying the type of middleware on the runtime. This attribute adds value to traces, giving the opportunity to visualise different kind of middleware using different representation in server-side. The supported values of type are `as` (application server), `ws` (web server), `dbs` (database server) or `mom` (message-oriented middleware). | `as` | No |
+| process.middleware.name | The name of the middleware running on this process. | `Tomcat` | No |
+| process.middleware.version | The version of the middleware of this process, as returned by the middleware (preferably during runtime) without modification. | `9.0.39` | No |
+| process.middleware.description | An additional description about the middleware of the process. | `Apache Tomcat/9.0.39` | No |
+
+`process.middleware.type` MUST be set to one of the values listed below. 
+`process.middleware.name` SHOULD be set to one of the values listed below. If none of the listed values apply, a custom value best describing the runtime MAY be used.
+
+***Application server middlewares:***
+
+Information describing the application server should be captured using the values acquired from the middleware specific API, preferably during runtime. As an example - for Java application servers this information can be captured by invoking `ServletContext.getServerInfo()` during runtime and parsing the result.
+
+Examples for some application server middlewares:
+
+| Name | `process.middleware.name` | `process.middleware.version` | `process.middleware.description` |
+| --- | --- | --- | --- |
+| Apache Tomcat | `Tomcat` | `9.0.39` | `Apache Tomcat/9.0.39` |
+| Eclipse Jetty | `Jetty` | `9.4.33` | `jetty/9.4.33.v20201020` |
+| Eclipse GlassFish | `GlassFish` | `5.0` | `GlassFish Server Open Source Edition  5.0` |
+| WildFly | `WildFly` | `21.0.0` | `WildFly Full 21.0.0.Final (WildFly Core 13.0.1.Final) - 2.2.2.Final` |
+
+***Web server middlewares:***
+
+Examples for some web server middlewares:
+
+| Name | `process.middleware.name` | `process.middleware.version` | `process.middleware.description` |
+| --- | --- | --- | --- |
+| nginx | `nginx` | `1.19.3` | `nginx version: nginx/1.19.3` |
+| Apache HTTP Server | `apache` | `2.4.41` | `Apache/2.4.41 (Ubuntu) OpenSSL/1.1.1f` |
+
+***Message-oriented middlewares:***
+
+Examples for some message-oriented middlewares:
+
+| Name | `process.middleware.name` | `process.middleware.version` | `process.middleware.description` |
+| --- | --- | --- | --- |
+| Apache Kafka | `Kafka` | `2.6.0` | `2.6.0 (Commit:62abe01bee039651)` |
+
+***Database middlewares:***
+
+Examples for some database middlewares:
+
+| Name | `process.middleware.name` | `process.middleware.version` | `process.middleware.description` |
+| --- | --- | --- | --- |
+| Apache Druid | `Druid` | `0.15.0` | `0.15.0-incubating` |
+| MySQL | `MySQL` | `5.7.28` | `5.7.28-0ubuntu0.19.04.2` |
+