[DOCS-11173] Add preview for OP API/TF (#29799)

* add preview

* move box

Author: maycmlee

content/en/observability_pipelines/set_up_pipelines/_index.md

@@ -23,8 +23,10 @@ further_reading:
 In Observability Pipelines, a pipeline is a sequential path with three types of components: source, processors, and destinations. The Observability Pipeline [source][1] receives logs from your log source (for example, the Datadog Agent). The [processors][2] enrich and transform your data, and the [destination][3] is where your processed logs are sent. For some templates, your logs are sent to more than one destination. For example, if you use the Archive Logs template, your logs are sent to a cloud storage provider and another specified destination.
 
 ## Set up a pipeline
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 {{< tabs >}}
 {{% tab "Pipeline UI" %}}
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 Set up your pipelines and its [sources][1], [processors][2], and [destinations][3] in the Observability Pipelines UI. The general setup steps are:
 
 1. Navigate to [Observability Pipelines][13].
@@ -61,9 +63,10 @@ After you have set up your pipeline, see [Update Existing Pipelines][11] if you
 [13]: https://app.datadoghq.com/observability-pipelines
 
 {{% /tab %}}
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 {{% tab "API" %}}
 
+<div class="alert alert-warning">Creating pipelines using the Datadog API is in Preview. Fill out the <a href="https://www.datadoghq.com/product-preview/observability-pipelines-api-and-terraform-support/"> form</a> to request access.</div>
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 You can use Datadog API to [create a pipeline][1]. After the pipeline has been created, [install the Worker][2] to start sending logs through the pipeline.
 
 Pipelines created using the API are read-only in the UI. Use the [update a pipeline][3] endpoint to make any changes to an existing pipeline.
@@ -75,6 +78,8 @@ Pipelines created using the API are read-only in the UI. Use the [update a pipel
 {{% /tab %}}
 {{% tab "Terraform" %}}
 
+<div class="alert alert-warning">Creating pipelines using Terraform is in Preview. Fill out the <a href="https://www.datadoghq.com/product-preview/observability-pipelines-api-and-terraform-support/"> form</a> to request access.</div>
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 You can use the [datadog_observability_pipeline][1] module to create a pipeline using Terraform. After the pipeline has been created, [install the Worker][2] to start sending logs through the pipeline.
 
 Pipelines created using Terraform are read-only in the UI. Use the [datadog_observability_pipeline][1] module to make any changes to an existing pipeline.