doc: Upgrade guide for v1.26.0 (#2992)

* 1.26 guide

* add mongodbatlas_search_index doc

* update search_index guide

* update search_index doc

* Update docs/guides/1.26.0-upgrade-guide.md

Co-authored-by: John Williams <[email protected]>

* Update docs/guides/1.26.0-upgrade-guide.md

Co-authored-by: John Williams <[email protected]>

* Update docs/guides/1.26.0-upgrade-guide.md

Co-authored-by: John Williams <[email protected]>

---------

Co-authored-by: Leo Antoli <[email protected]>
Co-authored-by: John Williams <[email protected]>

Author: 3 people

docs/guides/1.26.0-upgrade-guide.md

@@ -0,0 +1,25 @@
+---
+page_title: "Upgrade Guide 1.26.0"
+---
+
+# MongoDB Atlas Provider 1.26.0: Upgrade and Information Guide
+
+The Terraform MongoDB Atlas Provider version 1.26.0 has a number of new and exciting features.
+
+## New Resources, Data Sources, and Features
+
+- You can now manage AWS Privatelink connections to AWS Confluent using the new `mongodbatlas_stream_privatelink_endpoint` resource and corresponding data sources. To learn more, please review the [mongodbatlas_stream_privatelink_endpoint](https://registry.terraform.io/providers/mongodb/mongodbatlas/latest/docs/resources/stream_privatelink_endpoint) resource documentation.
+- You can now use AWS Privatelinks created with the `mongodbatlas_stream_privatelink_endpoint` resource as the Networking Access Type of a Kafka Stream Connection `mongodbatlas_stream_connection` resource. To learn more, see the [mongodbatlas_stream_connection](https://registry.terraform.io/providers/mongodb/mongodbatlas/latest/docs/resources/stream_connection#networking) resource documentation.
+- You can now disable a Backup compliance policy by deleting the `mongodbatlas_backup_compliance_policy` resource. To learn more, see the [mongodbatlas_backup_compliance_policy](https://registry.terraform.io/providers/mongodb/mongodbatlas/latest/docs/resources/backup_compliance_policy) resource documentation.
+
+## Breaking Changes
+
+- Due to recent updates in the API, `mongodbatlas_search_index` will now require target collections to exist before index creation.
+
+## Helpful Links
+
+* [Report bugs](https://github.com/mongodb/terraform-provider-mongodbatlas/issues)
+
+* [Request Features](https://feedback.mongodb.com/forums/924145-atlas?category_id=370723)
+
+* [Contact Support](https://docs.atlas.mongodb.com/support/) covered by MongoDB Atlas support plans, Developer and above.

docs/resources/search_index.md

@@ -144,7 +144,7 @@ analyzers = <<-EOF
 EOF
 ```
 
-* `collection_name` - (Required) Name of the collection the index is on.
+* `collection_name` - (Required) Name of the collection the index is on. **NOTE:** The collection must exist before creating the index.
 
 * `database` - (Required) Name of the database the collection is in.