Update docs/community/events/ambassadors_celebration_meeting_and_dinner.md, docs/community/events/images/ambass-celebration-2023-img-st-annes-coffee.png, docs/community/events/images/ambass-celebration-2023-img-amb-dinner.png

Hi there!

Thank you for the great theme! I am a happy user and was delighted to see that mermaid support has landed.

In some cases the usage of jsDelivr might not be possible for technical or compliance reasons.

This commit adds a second way to include the mermaid lib by specifying a path in the mermaid config. This way a local version of the lib can be used.

It should be fully backwards compatible, not requiring any action by users that already include the lib from the CDN.

I already added some documentation, but I am also happy to extend this, if this change is generally well-received.

Cheers,
Christian

In #1058, I noted:

> Tangentially related work:
> ...
> - better annotate new features (motivated by writing these docs)
>     - we should add "New" to new features :) 
>     - we should note when a feature was introduced (I think this is a core part of most software documentation)
>     - we should annotate things that are "Advanced" in so far as the average Just the Docs user will not use them / they require significant Jekyll knowledge
> 

This came up again in https://github.com/just-the-docs/just-the-docs/discussions/1136#discussioncomment-4716253, so I think it's best for us to resolve this sooner rather than later.

This PR is me doing that. I:

- have added a headings-level "New" label to every new heading introduced since `v0.3`
- added, when possible, inline YAML comments when new configuration options have been introduced

I did this by scanning through the CHANGELOG and selecting each feature that is either tagged with `Add` and has documentation.

I may have also missed any new features, so some double-checking would be helpful!