doc: Defines migration guide for 1.23.0 release (#2898)

* define migration guide for 1.23.0 release

* remove redudant new from changelog entries

* use full url

* docs review

Author: AgustinBettati

.changelog/2825.txt

@@ -1,11 +1,11 @@
-```release-note:note
-resource/mongodbatlas_advanced_cluster: Adds new `advanced_configuration.0.default_max_time_ms` attribute
+```release-note:enhancement
+resource/mongodbatlas_advanced_cluster: Adds `advanced_configuration.0.default_max_time_ms` attribute
 ```
 
-```release-note:note
-data-source/mongodbatlas_advanced_cluster: Adds new `advanced_configuration.0.default_max_time_ms` attribute
+```release-note:enhancement
+data-source/mongodbatlas_advanced_cluster: Adds `advanced_configuration.0.default_max_time_ms` attribute
 ```
 
-```release-note:note
-data-source/mongodbatlas_advanced_clusters: Adds new `advanced_configuration.0.default_max_time_ms` attribute
+```release-note:enhancement
+data-source/mongodbatlas_advanced_clusters: Adds `advanced_configuration.0.default_max_time_ms` attribute
 ```

docs/guides/1.23.0-upgrade-guide.md

@@ -0,0 +1,24 @@
+---
+page_title: "Upgrade Guide 1.23.0"
+---
+
+# MongoDB Atlas Provider 1.23.0: Upgrade and Information Guide
+
+The Terraform MongoDB Atlas Provider version 1.23.0 has a number of new and exciting features.
+
+## New Resources, Data Sources, and Features
+
+- You can now leverage auto-scaling to scale the instance size of each individual shard independently for sharded and geo-sharded clusters defined with `mongodbatlas_advanced_cluster`. To learn more, see the [Advanced Cluster New Sharding Configurations - Use Auto-Scaling Per Shard](https://registry.terraform.io/providers/mongodb/mongodbatlas/latest/docs/guides/advanced-cluster-new-sharding-schema#use-auto-scaling-per-shard).
+
+- You can now pin a cluster's FCV before upgrading in Atlas, which enables you to revert MongoDB to the previous version after upgrading without experiencing version compatibility issues. This is supported in `mongodbatlas_advanced_cluster` and `mongodbatlas_cluster` using `pinned_fcv`. To learn more, see either [mongodbatlas_advanced_cluster](https://registry.terraform.io/providers/mongodb/mongodbatlas/latest/docs/resources/advanced_cluster) or [mongodbatlas_cluster](https://registry.terraform.io/providers/mongodb/mongodbatlas/latest/docs/resources/cluster) resource documentation.
+
+- You can now configure the default time limit in milliseconds for individual read operations to complete in `mongodbatlas_advanced_cluster` using `advanced_configuration.0.default_max_time_ms`. To learn more, see [mongodbatlas_advanced_cluster](https://registry.terraform.io/providers/mongodb/mongodbatlas/latest/docs/resources/advanced_cluster) resource documentation.
+
+
+## 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.