Added instructions for upgrading OSS from 3.3.33 to 4.6.16

[vidarl]

Question	Answer
JIRA Ticket	https://issues.ibexa.co/browse/IBX-9638
Versions	3.3, 4.6
Edition	OpenSource

This adds instructions on how to upgrade from 3.3.33 to 4.6.16 ( Work on how to do it from 3.3.0 is also needed, but don't have time ATM)

Checklist

• [ ] Text renders correctly
• [ ] Text has been checked with vale
• [ ] Description metadata is up to date
• [ ] Redirects cover removed/moved pages
• [ ] Code samples are working
• [ ] PHP code samples have been fixed with PHP CS fixer
• [ ] Added link to this PR in relevant JIRA ticket or code PR