DataBackend has an undocumented dependency on the script binary in util-linux

I've configured my execute command logging to cloudwatch only:
```
execute_command_configuration = {
logging = "OVERRIDE"
log_configuration = {
cloud_watch_log_group_name = "/aws/ecs/something"
cloud_watch_encryption_enabled = false
}
}
```

However, when my ubi8 container did not have the script binary installed (in package util-linux), I received this error:
```
2026-01-14 10:51:41 ERROR [ssm-session-worker] [ecs-execute-command-egv8enfq3l9zptzgnrlq6szeji] [DataBackend] [pluginName=InteractiveCommands] unable to generate log data: Failed to generate transcript with the following errors:
exec: "script": executable file not found in $PATH:
```
As a result the ssm agent tried to log to s3 instead in a fallback mechanism, but s3 was not configured.

Certain containers running in ECS it might not install util-linux by default, so maybe this dependency should be documented.

Start by reviewing the DataBackend transcript-generation behavior and the documentation covering ECS execute-command logging. Document the requirement for the script binary from util-linux and explain the S3 fallback when CloudWatch logging cannot generate a transcript; done when container users can identify and install the dependency.

Written by the indexing model from the issue text.