Modify upload license error language

What does this MR do and why?

Part of https://gitlab.com/gitlab-org/gitlab/-/issues/349810

⚠ Depends on !79957 (merged) to be merged first. ⚠ Has to be in the same release as !79957 (merged).

Add clearer wording to the error messages when uploading a cloud license in the license upload form. While the error message won't show during the upload, the License model validation for an invalid license key is also slightly modified for a cloud license.

Screenshots or screen recordings

scenario	screenshot
before
after when uploading online cloud license
after with invalid offline license

How to set up and validate locally

New error message for uploading cloud license:

1. Copy the license key of a (online) cloud license.
2. Go to /admin/license/new in your GitLab instance.
3. Paste the copied license key into the text area for Enter license key.
4. Check the terms of service.
5. Submit the form
6. See the updated error message.

New error message for an invalid offline license:

1. Go to /admin/license/new in your GitLab instance.
2. Check the terms of service.
3. Submit the form without entering a license key or uploading a license file.
4. See the updated error message.

MR acceptance checklist

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