docs: add minimalist metamodel-export documentation

Author: nkoester

docs/global/modules/core/pages/howto/usage-model-api-gen-gradle.adoc

@@ -70,7 +70,7 @@ pluginManagement {
 [source,kotlin]
 --
 plugins {
-    id("org.modelix.metamodel.gradle")
+    id("org.modelix.model-api-gen")
 }
 
 val mpsVersion: String by rootProject

docs/global/modules/core/pages/reference/component-metamodel-export.adoc

@@ -1,2 +1,11 @@
 = MPS solution for metamodel-export
 :navtitle: `metamodel-export` (MPS)
+
+== Overview
+
+In order to export a meta-model (i.e. the structure aspect of a langauge) from MPS, modelix uses the MPS solution `metamodel-export`.
+This solution maps the structure of a language to corresponding serializable data classes of the `model-api`[https://api.modelix.org/2.3.0/model-api/org.modelix.model.data/index.html] (e.g. `LanguageData` and `ConcepData`).
+Further, the `metamodel-expor` provides a command line interface to export these data classes to a JSON file from outside of MPS.
+
+The `metamodel-export` is mainly used in the corresponding gradle plugin xref:core:reference/component-model-api-gen-gradle.adoc[model-api-gen-gradle].
+

docs/global/modules/core/pages/reference/component-model-api-gen-gradle.adoc

@@ -9,7 +9,7 @@ https://artifacts.itemis.cloud/#browse/browse:maven-mps:org%2Fmodelix%2Fmodel-ap
 --
 
 == Overview
-The `model-api-gen.gradle.plugin` is a Gradle plugin that wraps the functionality of xref:core:reference/component-model-api-gen.adoc[model-api-gen].
+The `model-api-gen.gradle.plugin` is a Gradle plugin that wraps the functionality of the xref:core:reference/component-metamodel-export.adoc[] and xref:core:reference/component-model-api-gen.adoc[].
 It provides an additional Gradle task which will apply a 2-staged process:
 
 . MPS metamodel export to JSON (optional)
@@ -26,7 +26,7 @@ metamodel {
     jsonDir = File("path/to/json/dir")
 }
 --
-As a result, all MPS-specific configuration settings will be ignored and the specified directory will be used for the next step. 
+As a result, all MPS-specific configuration settings will be ignored and the specified directory will be used for the next step.
 
 . JSON to model API generation
 +
@@ -195,4 +195,4 @@ metamodel {
         languageClass.suffix = "MyLanguageSuffix"
     }
 }
---
+--