KTOR-6519 Get started with Ktor Server tutorials restructuring

[vnikolova]

KTOR-6519 The new tutorials under "Get started with Ktor Server" are now complete.

1. Handle requests and generate responses - replaces the first part of the previous "Creating HTTP APIs" tutorial
2. Create RESTful APIs - replaces the second part of the "Creating HTTP APIs" tutorial
3. Build a web application- replaces the "Creating a static website" and "Creating an interactive website" tutorials
4. Create a WebSocket application - replaces the "Creating a WebSocket chat" tutorial and makes the "Creating a WebSocket chat client" tutorial redundant.
5. Integrate a database - replaces the tutorials under Database Integration: "Database persistence with exposed" and "Connection pooling and caching"

Affected topics:

• Docker Compose - the tutorial has been updated to start from the project created in the "Integrate a Database" tutorial
• Welcome page