Improve taxonomies and tags

[cjyabraham]

Here is some feedback on our tags that came from the Ambassadors. I'm not sure which need to be actioned at this point:
- Someone was confused by the “Ambassador” tag; it’s not clear to them that this meant the presentation was delivered by an Ambassador
- Can we have a tag for “Beginner”, “Intermediate”, “Advanced” to allow people to filter by difficulty of the material?
- Is the Projects taxonomy limited to just CNCF projects or could we also list tools like Jenkins or other LF projects?
- How many tags are allowed for a presentation?
- Have a Presentation Format taxonomy with “Tutorial”, “Keynote”, …