Extend AWS support for temporary tokens [SRTSR-47] (#309)

This updates interfaces for supporting temporary tokens in AWS.

Tested this locally and it seems to enforce it if providing a list vs a
string:

```
semgrep error: Invalid rule schema
['list1', 'list2'] is not of type 'string'
```

General checklist doesn't apply since we aren't updating an .atd for
this.

rule_schema_v1.yaml

@@ -76,6 +76,8 @@ $defs:
         type: string
       region:
         type: string
+      session_token:
+        type: string
     required: [ access_key_id, secret_access_key, region ]
   # EXPERIMENTAL
   http-request-content: