ra3-migration-replay fails to set target endpoint and region

Encountering multiple errors when running the ra3-migration-replay:

### 1. Replacement for `target_cluster_endpoint` is failing:
```
Error:[INFO] 2022-02-16 14:50:25 Loading config file from ./2022-02-16-13-52-33/replay_target.yaml
[INFO] 2022-02-16 14:50:25 Saving SimpleReplay logs to simplereplay_logs
[INFO] 2022-02-16 14:50:25 Logging to simplereplay_logs/replay.log
[INFO] 2022-02-16 14:50:25 Version 2.2
Traceback (most recent call last):
File "replay.py", line 1856, in
main()
File "replay.py", line 1615, in main
cluster = cluster_dict(g_config["target_cluster_endpoint"])
File "/amazonutils/amazon-redshift-utils/src/SimpleReplay/util.py", line 175, in cluster_dict
"region": url_split[2],
IndexError: list index out of range
failed to run commands: exit status 1
```

The problem is that this [line](https://github.com/awslabs/amazon-redshift-utils/blob/3399cc27ebc1ca8a68ee9d8acda6b3ca8637f653/src/SimpleReplay/cloudformation/run_replay.sh#L25) does NOT actually perform a replacment: `sed -i "s#target_cluster_endpoint: \"\"#target_cluster_endpoint: \"$cluster_endpoint\"#g" ./$bucket_keyprefix/replay_target.yaml`

Because the default value for `target_cluster_endpoint` was [recently changed](https://github.com/awslabs/amazon-redshift-utils/commit/a96f6047128399bfc4a98467ea5cde4b29122937#diff-8d396c1a1bb521c0fcbe011e083267ca05ca9d245a4f6b7ec4df3a6c04ef2549R8) from `""` to `"host:port/database"`

Fix:
```
sed -i "s#target_cluster_endpoint: \"host:port/database\"#target_cluster_endpoint: \"$cluster_endpoint\"#g" ./$bucket_keyprefix/replay_target.yaml
```

### 2. `target_cluster_region` defaults to an empty string, causing: `ValueError: Invalid endpoint: https://redshift..amazonaws.com`

Why was this variable introduced? It would be better to parse the region from `target_cluster_endpoint` [using same logic as seen in util.py](https://github.com/awslabs/amazon-redshift-utils/blob/3399cc27ebc1ca8a68ee9d8acda6b3ca8637f653/src/SimpleReplay/util.py#L185)

Full error:
```
Traceback (most recent call last):
File "replay.py", line 1856, in
main()
File "replay.py", line 1745, in main
get_connection_credentials(connection_logs[0].username, database=connection_logs[0].database_name, max_attempts=1)
File "replay.py", line 1338, in get_connection_credentials
rs_client = client("redshift", region_name=g_config.get("target_cluster_region", None), **additional_args)
File "/usr/local/lib/python3.7/site-packages/boto3/__init__.py", line 93, in client
return _get_default_session().client(*args, **kwargs)
File "/usr/local/lib/python3.7/site-packages/boto3/session.py", line 275, in client
aws_session_token=aws_session_token, config=config)
File "/usr/local/lib/python3.7/site-packages/botocore/session.py", line 874, in create_client
client_config=config, api_version=api_version)
File "/usr/local/lib/python3.7/site-packages/botocore/client.py", line 93, in create_client
verify, credentials, scoped_config, client_config, endpoint_bridge)
File "/usr/local/lib/python3.7/site-packages/botocore/client.py", line 362, in _get_client_args
verify, credentials, scoped_config, client_config, endpoint_bridge)
File "/usr/local/lib/python3.7/site-packages/botocore/args.py", line 108, in get_client_args
proxies_config=new_config.proxies_config)
File "/usr/local/lib/python3.7/site-packages/botocore/endpoint.py", line 335, in create_endpoint
raise ValueError("Invalid endpoint: %s" % endpoint_url)
ValueError: Invalid endpoint: https://redshift..amazonaws.com
failed to run commands: exit status 1
```

Start with src/SimpleReplay/cloudformation/run_replay.sh around line 25 and inspect the generated replay_target.yaml replacement. Then read src/SimpleReplay/util.py around cluster_dict and replay.py around the target-region client setup. Done means the endpoint replacement matches the current default and replay no longer constructs an empty-region Redshift endpoint when using the target cluster configuration.

Written by the indexing model from the issue text.