feat: add webui backend to rock

[patriciareinoso]

Description

The Rock container image for the NMS should contain both the Next.JS frontend (NMS) and backend components (WebUI).

This PR:

• Build the frontend
• Copy the static files over to the webconsole/ui/frontend_files directory
• Build the backend with the ui go build tag.

Remove integration tests: webui is the service that runs on the rock. We cannot test that we have access to the UI as before because, in order to get the webui up and running it needs to connect to mongoDB. If the connection fails, an exception is raised.

This PR depends on:

• feat: Add static file serving support in webconsole omec-project/webconsole#191
• feat: use webui API in NMS #619
• feat: config gNBs and UPFs omec-project/webconsole#194

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code.
• I have made corresponding changes to the documentation.
• I have added tests that validate the behaviour of the software.
• I validated that new and existing unit tests pass locally with my changes.
• Any dependent changes have been merged and published in downstream modules.

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