docs: move Server recipes to how-to guides

[bajtos]

At the moment, the Server page in "Behind the scenes" is mixing explanations with how-to guides. This makes it difficult for our users to find the relevant content (a recipe to achieve the outcome they want).

As part of our adoption of the four-quadrant documentation system (see #5549 and #5718), we should extract all guides from explanation pages into guide pages (see #5768 for inspiration) and keep explanation pages focused on explaining the concepts & providing background information.

This story is a part of Epic #5783 move recipes to how-to guides.

Acceptance criteria

Move the following recipes into "How-to guides", decide yourself whether to create a new page for each recipe or group multiple recipes in one page. For each recipe moved elsewhere, add a new entry to "Common task" list in the "Server" page.

• Configure REST API Explorer, including Disable redirect to API Explorer and Use a self-hosted API Explorer
• Customize CORS
• Customize express settings
• Configure the base path
• Configure the router
• Configure the request body parser options
• Add servers to application instance
• Enhance OpenAPI Specification

[mrmodise]

I will take this on. Thanks