Print a warning when an ignored option is used

[jamest-gaia]

Describe the feature

Print a warning to the operator when receiving an option that is ignored.
E.g.

$ aws s3 ls --output json
**ignoring option --output, see aws s3 ls help` for more info**
2020-12-21 14:58:42 mybucket-name
2021-04-14 13:55:06 mybucket2-name
etc..

Use Case

I need this feature because I was frustrated trying to get json output from the aws s3 ls command using the documented --output option. I only became aware it was not supported after searching and finding #709

Proposed Solution

If I use an option that is ignored such as --output on aws s3 please print a warning to let me know that.

Other Information

See #709

Acknowledgements

• I may be able to implement this feature request
• This feature might incur a breaking change

CLI version used

2.11.26

Environment details (OS name and version, etc.)

Linux/5.10.16.3-microsoft-standard-WSL2 exe/x86_64.debian.11

[tim-finnigan]

Thanks @jamest-gaia for reaching out. I understand your frustration about the --output command being ignored in this scenario. I recently opened a related issue here to document this inconsistency: #7634. Because these issues call out the same underlying problem, I think we should consolidate them for tracking purposes. But I will reference your suggestion to add a warning in that issue.

[github-actions]

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