Docs/WPB-22269 add architecture overview

[MarianKijewski]

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PR Submission Checklist for internal contributors

• The PR Title

  • conforms to the style of semantic commits messages¹ supported in Wire's Github Workflow²
  • contains a reference JIRA issue number like SQPIT-764
  • answers the question: If merged, this PR will: ... ³

• The PR Description

  • is free of optional paragraphs and you have filled the relevant parts to the best of your ability

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What's new in this PR?

Issues

No clear way of understanding how SDK interacts with App and Backend, as well as no explanation of how different inner components communicate.

Solutions

Write architecture section with diagram.

Testing

How to Test

Run npm ci and npm start. Navigate to http://localhost:3000/core-concepts/architecure and see the content.

Notes

This PR contains 2 to-dos to add links to WireApplicationManager reference and the Showcase sections once added.

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References

1. https://sparkbox.com/foundry/semantic_commit_messages
2. https://github.com/wireapp/.github#usage
3. E.g. feat(conversation-list): Sort conversations by most emojis in the title #SQPIT-764.

[spoonman01]

Adapt to alpha-numerical ordering after my PR is merged.
Decide where the core-concepts should be in the order and add a relevant category.json for the name.

I like adding the mermaid but as we talked we need to make it more clear. It's hard for me to suggest how.
One idea is to not have both EventsRouter and EventListener. Maybe just keeping the router is enough of an abstraction.
Also I would remove the connection between DevInterface -- domain objects --> Crypto. While correct it is ambiguous and the developer should not really care.

Ultimately, nitpicking a bit, I would flip the grapth vertically. For me it makes way more sense to have the "Wire Backend" on the top, SDK in the middle and "Developer Application" at the bottom