Auto Snapshots to Azure Storage document addition (#704)

Commit docs missing azure_auth_mode "environment" method

Azure authentication details are retrieved from the environment
variables: AZURE_CLIENT_ID, AZURE_CLIENT_SECRET, AZURE_TENANT_ID, and
AZURE_SUBSCRIPTION_ID if "environment" method is set.

Author: catalinasmeureanu

content/vault/v1.18.x/content/api-docs/system/storage/raftautosnapshots.mdx

@@ -140,7 +140,7 @@ parameters in the context of AWS EKS & S3 configuration.
 
 - `azure_account_name` `(string)` - Azure account name.
 
-- `azure_auth_mode` `(string)` - One of `shared` or `managed`.
+- `azure_auth_mode` `(string)` - One of `shared`, `managed`, or `environment`. If `environment` is set, Azure authentication details are retrieved from the environment variables: `AZURE_CLIENT_ID`, `AZURE_CLIENT_SECRET`, `AZURE_TENANT_ID`, `AZURE_SUBSCRIPTION_ID`. 
 
 - `azure_account_key` `(string)` - Azure account key. Used for `shared` authentication.
 

content/vault/v1.19.x/content/api-docs/system/storage/raftautosnapshots.mdx

@@ -140,7 +140,7 @@ parameters in the context of AWS EKS & S3 configuration.
 
 - `azure_account_name` `(string)` - Azure account name.
 
-- `azure_auth_mode` `(string)` - One of `shared` or `managed`.
+- `azure_auth_mode` `(string)` - One of `shared`, `managed`, or `environment`. If `environment` is set, Azure authentication details are retrieved from the environment variables: `AZURE_CLIENT_ID`, `AZURE_CLIENT_SECRET`, `AZURE_TENANT_ID`, `AZURE_SUBSCRIPTION_ID`. 
 
 - `azure_account_key` `(string)` - Azure account key. Used for `shared` authentication.
 

content/vault/v1.20.x/content/api-docs/system/storage/raftautosnapshots.mdx

@@ -140,7 +140,7 @@ parameters in the context of AWS EKS & S3 configuration.
 
 - `azure_account_name` `(string)` - Azure account name.
 
-- `azure_auth_mode` `(string)` - One of `shared` or `managed`.
+- `azure_auth_mode` `(string)` - One of `shared`, `managed`, or `environment`. If `environment` is set, Azure authentication details are retrieved from the environment variables: `AZURE_CLIENT_ID`, `AZURE_CLIENT_SECRET`, `AZURE_TENANT_ID`, `AZURE_SUBSCRIPTION_ID`. 
 
 - `azure_account_key` `(string)` - Azure account key. Used for `shared` authentication.