fix(api): add api initialization notice

[gacevicljubisa]

Checklist

• I have read the coding guide.
• My change requires a documentation update, and I have done it.
• I have added tests to cover my changes.
• I have filled out the description and linked the related issues.

Description

This PR addresses issue #4734 by improving the behavior of the Bee API during the node initialization process. Previously, when the node was syncing batch data, the API appeared to be inaccessible, providing no indication of the ongoing sync process. Now, all routes are mounted immediately, but some may be temporarily disabled during initialization, returning appropriate status codes.

Changes

• 503 Service Unavailable: Routes that are disabled during the syncing phase now return a 503 Service Unavailable status with the message:
  "Node is syncing. This endpoint is unavailable. Try again later."
  Once the syncing is complete, the routes will be enabled and respond normally.

• 501 Not Implemented: If the swapEnabled or chequebookEnabled flags are set to false, routes that depend on these features will now return a 501 Not Implemented status.

• 404 Not Found: Any routes that do not exist will return a 404 Not Found status.

Open API Spec Version Changes (if applicable)

Motivation and Context (Optional)

This change improves the user experience by providing clear feedback during node initialization, preventing confusion when the API appears to be inaccessible. It ensures that users are informed about the node's state and can understand why certain API routes may not be available temporarily.

How it works

• All routes are mounted immediately but may not be active depending on the node's state.
• Disabled routes return 503 until they are enabled once the sync is complete.
• Feature-dependent routes (like those for Swap and Chequebook) return 501 if the corresponding feature is disabled.
• Invalid or non-existent routes return a 404 as expected.

Related Issue (Optional)

#4734

Screenshots (if appropriate):

[istae]

why have an option if we can explicitly enable the the full API using EnableFullAPI()

[gacevicljubisa]

Initial idea to provide options is for unit testing purposes. Was considering to add WithFullAPIDisabled option as well. And then expand testServerOptions in api_test.go.
Also it can be used in one line to mount and enable apiService.Mount(api.WithFullAPI()), which is the case in devnode.go

[gacevicljubisa]

Option is removed

[istae]

Great work!

[janos]

👏