Add embed option to share modal

[farisd16]

This PR adds the embed option to the share modal.

Upon clicking on embed, a text of two lines is copied to the clipboard. If the text is pasted in a pull request / issue, an image of the diagram together with a link to editing a copy can be seen.

This is a screenshot of an example embedding in #98 coming from a test server of Apollon:

In the future, when version management of diagrams is implemented, as described in #97, the embedding will display the newest version of a diagram.

[FelixTJDietrich]

Hmm, basically everyone uses GitHub using dark mode, we should add a background 🤔

Also maybe you can switch around the buttons:
Edit, Embed, Collaborate
Give Feedback, See Feedback

This might be better what do you think?

[FelixTJDietrich]

Why are the recently shared diagrams separate? Do you copy each part? I thought we add an additional "Recently shared embed" if it exists and have one button that copies the markdown text for the whole embed

[egenerse]

I tested and it works, I see the screen shot of the diagram in the github issue after pasting it

[FelixTJDietrich]

IMO this should read Copy Embed for embeddings and Copy Link for just the shared links of edit, collaborate, see feedback, and give feedback

[FelixTJDietrich]

Worked as expected when testing on the consolidated branch, code looks also good to me