Adding CentOS EOL caution

[rayoef]

[learn-build-service-prod[bot]]

Learn Build status updates of commit 228e38e:

:white_check_mark: Validation status: passed

File	Status	Preview URL	Details
docs-ref-conceptual/includes/cli-install-linux-dnf.md	:white_check_mark:Succeeded	View
docs-ref-conceptual/install-azure-cli.md	:white_check_mark:Succeeded	View
docs-ref-conceptual/use-azure-cli-successfully.md	:white_check_mark:Succeeded	View

For more details, please refer to the build report.

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[rayoef]

#sign-off

This PR is part of a bulk update to include an end-of-life message about CentOS.

Please merge.

[rayoef]

#sign-off

This PR is part of a bulk update to include an end-of-life message about CentOS.

Please merge.