[docs] /create documentation and minor refactoring

docs/api.md

@@ -0,0 +1,43 @@
+## Serverledge API Reference
+
+
+<!--
+
+<details>
+ <summary><code>POST</code> <code><b>/create</b></code> <code>(registers a new function)</code></summary>
+ Details
+</details>
+-->
+
+
+### Registering a new function
+
+ <code>POST</code> <code><b>/create</b></code> <code>(registers a new function)</code>
+
+##### Parameters
+
+> | name      |  required   | type               | description                                                           |
+> |-----------|-------------|-------------------------|------------|
+> | `Name`    |         yes | string  | Name of the function (globally unique)  |
+> | `Runtime`         | yes | string  | Base container runtime (e.g., `python310`)
+> | `MemoryMB`        | yes | int     | Memory (in MB) reserved for each function instance
+> | `CPUDemand`       |     | float   | Max CPU cores (or fractions of) allocated to function instances (e.g., `1.0` means up to 1 core, `-1.0` means no cap)
+> | `Handler`         | (yes)    | string  | Function entrypoint in the source package; syntax and semantics depend on the chosen runtime (e.g., `module.function_name`). Not needed if `Runtime` is `custom`
+> | `TarFunctionCode` | (yes)    | string  | Source code package as a base64-encoded TAR archive. Not needed if `Runtime` is `custom`
+> | `CustomImage`     |     | string  | If `Runtime` is `custom`: custom container image to use
+
+
+##### Responses
+
+> | http code     | content-type                      | response                        | comments                                    |
+> |---------------|-----------------------------------|---------------------------------|-----------------------------------|
+> | `200`         | `application/json`        | `{ "Created": "function_name" }`    |                            |
+> | `404`         | `text/plain`              | `Invalid runtime.` |    Chosen `Runtime` does not exist      |
+> | `409`         | `text/plain`              |  |    Function already exists                        |
+> | `503`         | `text/plain`              |  |    Creation failed                        |
+
+
+
+------------------------------------------------------------------------------------------
+
+#### Listing existing stubs & proxy configs as YAML string

internal/api/api.go

@@ -127,7 +127,7 @@ func CreateFunction(c echo.Context) error {
 	_, ok := function.GetFunction(f.Name) // TODO: we would need a system-wide lock here...
 	if ok {
 		log.Printf("Dropping request for already existing function '%s'\n", f.Name)
-		return c.JSON(http.StatusConflict, "")
+		return c.String(http.StatusConflict, "")
 	}
 
 	log.Printf("New request: creation of %s\n", f.Name)