chore: add user name character warning

[kstribrnAmzn]

Issue #, if available:

Description of changes:
Adds a warning log when potentially
invalid characters are used in a username.

Why is this change necessary:

How was this change tested:

• Updated or added new unit tests.
• Updated or added new integration tests.
• Updated or added new end-to-end tests.
• If my code makes a remote network call, it was tested with a proxy.

Any additional information or context required to review the change:
This change aims to raise awareness around invalid user names which can cause component failures.
For Linux see this (best doc I could find).
For Windows see this.
Documentation Checklist:

• Updated the README if applicable.

Compatibility Checklist:

• I confirm that the change is backwards compatible.
• Any modification or deletion of public interfaces does not impact other plugin components.
• For external library version updates, I have reviewed its change logs and Nucleus does not consume
  any deprecated method or type.

Refer to Compatibility Guidelines for more information.

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.

[kstribrnAmzn]

To test this change I deployed the nucleus onto a windows instance and attempted to boot it up with the following command

java -Droot="C:\Users\Administrator\aws.greengrass.nucleus" "-Dlog.store=FILE" -jar .\aws.greengrass.nucleus\lib\Greengrass.jar --aws-region us-west-2 --thing-name windowsWarnThing --component-default-user ggc_group:ggc_user

Log message seen in the greengrass.log file

2025-05-01T15:54:54.800Z [INFO] (main) com.aws.greengrass.security.SecurityService: Register crypto key service provider. {keyType=file}
2025-05-01T15:54:54.800Z [INFO] (main) com.aws.greengrass.security.SecurityService: Register MQTT connection security provider. {keyType=file}
2025-05-01T15:54:54.803Z [WARN] (main) com.aws.greengrass.lifecyclemanager.KernelCommandLine: Component user may contain invalid characters. This can cause issues starting a component.. {}
2025-05-01T15:54:54.842Z [INFO] (main) com.aws.greengrass.lifecyclemanager.Kernel: Successfully setup Nucleus launch parameters. {}
2025-05-01T15:54:55.049Z [INFO] (main) com.aws.greengrass.lifecyclemanager.Kernel: Nucleus lifecycle has been initialized successfully. {}

[alter-mage]

LGTM but how are you creating this pull request? Are you creating a fork of this repo and creating a PR out of that? That will not work as it will not be able to run the CI for unit and integ tests. You need clone this repo, create a new branch for your work and create a PR from that.