Add Rclone provider in backup destination creation workflow

[DavidePrincipi]

Implement new backup destination type "Rclone compatible provider" in the creation workflow, following the UI described in issue #7902:

UI/UX design

See https://www.figma.com/design/OsYqPXdkKJz0tBJRsiQgAf/NethServer-shared-file?node-id=4400-13382&t=tjGccaRHOV8MIySR-4

Change summary

Items with ⚠️ are not present in the Figma mockup.

1. Remove "See details" modal.
2. "Edit" is the default action for backup destinations.
3. Data encryption key field is visible as read-only under the Advanced section of the Edit form. ⚠️
4. Remove Azure provider - retain other providers, apply minor icon tweaks.
5. For the new "Rclone configuration" destination:
   a) Provide textarea for rclone config
   b) Support .conf file upload
   c) Add Path (optional) text input field. Place it between the upload-textarea and the Destination name field ⚠️
   d) Destination name field
   e) Advanced section for the Data encryption key in read-only. ⚠️
6. In the restoration workflow, in the snapshot selection list, display the backup snapshot size. ℹ️ Figma mockup
7. Password values are not shown in Edit; empty means "Unchanged", consistent with SMTP routes in Mail module. -- ✅ implemented by feat(backup): route all backup traffic through rclone-gateway ns8-core#1175

See also

• NS8 backup destination management #7902
• https://mattermost.nethesis.it/nethesis/pl/qwikfse81br39jtbkfjr4cdkeo (Design Backup Destination Management)
• https://mattermost.nethesis.it/nethesis/pl/z5mnqbtktbgmbeddbqkr96qbqc (Backup Details and backup ID)

This is the Advanced > Data encryption key preview, that is missing in the mockup

[stephdl]

QA

Tested on core:3.20.0-dev.12.

1 - Open Backup and verify the destination creation flow:

• Azure is no longer available.
• Rclone compatible provider is available in the provider list.
• The default action for a destination is Edit and the old See details modal is no longer present.

2 - Create a new Rclone compatible provider destination:

• Verify both configuration methods:

  • paste the configuration into the textarea
  • upload the same configuration from a .conf or .txt file

• Verify the optional Path field is available between the configuration input and Destination name.

• Verify validation errors are shown for invalid or empty configuration.

• Example test for an SMB-based rclone destination:

  • create a Samba share
  • inspect an existing generated configuration with:

    runagent -m node cat rclone/rclone.conf

  • use a single remote section such as:

    type = smb
    host = 192.168.xxx.xxx
    user = xxxx
    pass = Sm0Zv9iIFkYZfSRfePNC
    domain = xxx

  • paste it into the textarea or upload it as a file (.conf or .txt), then save the destination, test the errors of rclone configuration

3 - Edit an existing destination:

• verify Data encryption key is visible with a widget to copy it under Advanced
• verify secret fields are not prefilled; leaving them empty means unchanged
• for Rclone destinations, verify it is possible to keep the current configuration, paste a new one, or upload a new file

4 - For SMB destinations:

• verify the informational warning about SMB2/SMB3 only is shown

5 - In the restore workflow:

• verify the snapshot list shows the snapshot size
• verify the most recent snapshot is clearly highlighted

6 - Verify destination deletion flow:

• a warning explains that scheduled backups using the destination will be removed
• existing backup data remains on the storage
• The UI suggests downloading the cluster backup to preserve access to the encryption key