OSDOCS-13803: Add Thailand AWS region support

Author: sslocket

modules/installation-aws-regions.adoc

@@ -29,6 +29,7 @@ The following AWS public regions are supported:
 * `ap-southeast-3` (Jakarta)
 * `ap-southeast-4` (Melbourne)
 * `ap-southeast-5` (Malaysia)
+* `ap-southeast-7` (Thailand)
 * `ca-central-1` (Central)
 * `ca-west-1` (Calgary)
 * `eu-central-1` (Frankfurt)