Support for European Sovereign Cloud (eusc-de-east-1)

**Is your feature request related to a problem? Please describe.**

When using the toolkit from an azure pipeline with a service connection using OIDC the sts endpoint that the toolkit uses is the wrong one. It points to `sts.eusc-de-east-1.amazonaws.com` and not `.eu`

**Describe the solution you'd like**

I like to have the toolkit support the new region in the European Sovereign Cloud (eusc-de-east-1)

**Describe alternatives you've considered**

N/A

**Additional context**

Logs:

```text
at constructor. (/home/vsts/work/_tasks/AWSCLI_/1.24.0/AWSCLI.js:37:133950)
at constructor.callListeners (/home/vsts/work/_tasks/AWSCLI_/1.24.0/AWSCLI.js:37:97340)
at constructor.emit (/home/vsts/work/_tasks/AWSCLI_/1.24.0/AWSCLI.js:37:97048)
at constructor.emitEvent (/home/vsts/work/_tasks/AWSCLI_/1.24.0/AWSCLI.js:38:28344)
at u (/home/vsts/work/_tasks/AWSCLI_/1.24.0/AWSCLI.js:37:130543)
at ClientRequest. (/home/vsts/work/_tasks/AWSCLI_/1.24.0/AWSCLI.js:61:16997)
at ClientRequest.emit (node:events:524:28)
at ClientRequest.emit (node:domain:489:12)
at emitErrorEvent (node:_http_client:101:11)
at TLSSocket.socketErrorListener (node:_http_client:504:5) {
code: 'UnknownEndpoint',
region: 'eusc-de-east-1',
hostname: 'sts.eusc-de-east-1.amazonaws.com'
```

No repository files or tests are named. Start by tracing how the toolkit derives the STS hostname for region eusc-de-east-1 and compare it with the European Sovereign Cloud endpoint; done means Azure Pipeline OIDC requests use the correct .eu hostname without UnknownEndpoint errors.

Written by the indexing model from the issue text.