Update Changelog for 3.18.0 release (#1938)

CHANGELOG.md

@@ -1,3 +1,12 @@
+## 3.18.0 (Jul 12, 2023)
+FEATURES:
+* Add support to set default issuers configuration for PKI Secrets Engine: ([#1937](https://github.com/hashicorp/terraform-provider-vault/pull/1937))
+* Add new `auth_login_token_file` method: ([#1928](https://github.com/hashicorp/terraform-provider-vault/pull/1928))
+* Update HTTP transport wrapper to support TLSConfig cloning: ([#1926](https://github.com/hashicorp/terraform-provider-vault/pull/1926))
+
+BUGS:
+* secrets/pki: fix server_flag being ignored: ([#1933](https://github.com/hashicorp/terraform-provider-vault/pull/1933))
+
 ## 3.17.0 (June 21, 2023)
 FEATURES:
 * Add support for multi-issuer functionality to PKI: ([#1910](https://github.com/hashicorp/terraform-provider-vault/pull/1910))