make kfp dependency optional in build and during runs

docs/source/getting_started/installation.md

@@ -33,12 +33,15 @@ The instructions below are installing the latest release.
 
 Prior to version 3.1, the `elyra` package included all dependencies. Subsequent releases allow for selective dependency installation:
 
-- `elyra` - install the Elyra core features
+- `elyra` - install the Elyra core features (except kfp dependencies)
 - `elyra[all]` - install core features and all dependencies
+- `elyra[airflow]` - install the Elyra core features and support for [Apache Airflow pipelines](https://github.com/apache/airflow)
+- `elyra[airflow-gitlab]` - install the Elyra core features and GitLab support for [Apache Airflow pipelines](https://github.com/apache/airflow)
+- `elyra[kfp]` - install the Elyra core features and support for [Kubeflow Pipelines](https://github.com/kubeflow/pipelines)
 - `elyra[kfp-tekton]` - install the Elyra core features and support for [Kubeflow Pipelines on Tekton](https://github.com/kubeflow/kfp-tekton)
-- `elyra[gitlab]` - install the Elyra core features and GitLab support for Apache Airflow pipelines
 - `elyra[kfp-examples]` - install the Elyra core features and [Kubeflow Pipelines custom component examples](https://github.com/elyra-ai/examples/tree/main/component-catalog-connectors/kfp-example-components-connector)
 
+
 ### pip
 
 If you use `pip`, install Elyra with:
@@ -94,7 +97,7 @@ conda install -c conda-forge "elyra[all]"
 ```
 
 **NOTE:**
-The Elyra packaging process was changed in version 3.1.0. The [Kubeflow Pipelines on Tekton](https://github.com/kubeflow/kfp-tekton) dependency [is no longer installed by default](https://github.com/elyra-ai/elyra/pull/2043). To install this dependency, you must specify `elyra[all]` or `elyra[kfp-tekton]`.
+The Elyra packaging process was changed in version 4.0. The [Apache Airflow pipelines](https://github.com/apache/airflow) or [Kubeflow Pipelines on Tekton](https://github.com/kubeflow/kfp-tekton) dependencies are no longer installed by default. To install this dependency, you must specify `elyra[all]`, `elyra[kfp]` or `elyra[kfp-tekton]`.
 
 You can also install the Pipeline editor, Code Snippet, Code Viewer, or Script editor extensions individually:
 

pyproject.toml

@@ -86,6 +86,12 @@ test = [
     "requests-unixsocket",
     "kfp-tekton"
 ]
+airflow = [
+
+]
+airflow-gitlab = [
+    "python-gitlab"
+]
 kfp = [
     "kfp>=1.7.0,<2.0,!=1.7.2",  # We cap the SDK to <2.0 due to possible breaking changes
     "typing-extensions>=3.10,<5",  # Cap from kfp
@@ -96,9 +102,6 @@ kfp-tekton = [
 kfp-examples = [
     "elyra-examples-kfp-catalog"
 ]
-gitlab = [
-    "python-gitlab"
-]
 # The following is a collection of "non-test" extra dependencies from above.
 all = [
     "kfp>=1.7.0,<2.0,!=1.7.2",  # We cap the SDK to <2.0 due to possible breaking changes