Generate canonical url and remove trailing slash

What does this MR do?

This MR adds a canonical link when the url ends in /. This canonical link removes the trailing slash because for SEO crawlers pages /foo and /foo/ are two different ones, but adding the canonical URL removes that duplicity.

That last statement is valid for inner pages but, for the main domain, it doesn't matter whether it has a trailing slash or not, they're not considered different pages.

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Separation of EE specific content

Related to #36820 (closed)