change pipeline to tenantPipeline

- release-service now expects `tenantPipeline` instead of `pipeline`
- using `pipeline` results in an `unknown field error` which leads to user confusion
- change `pipeline` to `tenantPipeline` to reflect the release-service change

docs/modules/ROOT/pages/advanced-how-tos/releasing/tenant-release-pipelines.adoc

@@ -43,7 +43,7 @@ spec:
        - name: demo-component-2
          repository: registry/destination-image-repository-2
          tags: [latest]
- pipeline:
+ tenantPipeline:
    pipelineRef: <.>
      resolver: git
      params: