Add endpoint override for eu-isoe-* region

[trivikr]

Internal JS-5117

Testing

import AWS from "../aws-sdk-js/lib/aws.js";

const client = new AWS.STS({ region: "eu-isoe-west-1" });
console.log(client.endpoint);

Verified with three services:

• STS: sts.eu-isoe-west-1.cloud.adc-e.uk
• S3: s3.eu-isoe-west-1.cloud.adc-e.uk
• DynamoDB: dynamodb.eu-isoe-west-1.cloud.adc-e.uk

Checklist

• [x] changelog is added, npm run add-change