Remove legacy license link from subscription page

What does this MR do and why?

• Remove "Upload a license file" link from subscription page (when instance is without a license)
• Remove "Upload license" button from subscription page (when instance has active license)
• Adds "License file" section to admin > settings with a link to upload a license file
• Updates the docs to reflect the new changes

Screenshots or screen recordings

area	before	after
admin > settings
admin > subscription (with active license)
admin > subscription (with active license)

How to set up and validate locally

• Checkout the branch
• Login with root user and navigate to the admin area
• Go to "Subscription" page
• Remove the license if you have (make sure to have the license file to upload it again afterward), observe "Activate subscription" block without "Upload a license file" link
• Upload the license again, go to the "Subscription" page again, observe the "Subscription details" block without "Upload license" button

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #348750