Describe the bug
In the web UI the section plans shows as child nodes of a given plan a list of snapshots from different hosts, without any indication by which host the snapshot was created. This can lead to confusion (if content of a snapshot does not match expectation) and potential data loss (if a snapshot seems to be unnecessary and gets deleted by a user).

To Reproduce
Steps to reproduce the behavior:

1. Install backrest on host1 with installation id host1
2. Add repository with id repo on a NAS
3. Add plan with id home to backup the home dir of host1 and run backup
4. Install backrest on host2 with installation id host2
5. Add repository with id repo on a NAS (existing repository is reused)
6. Add plan with id home to backup the home dir of host2 and run backup
7. Open Web UI on host1, navigate to plans section, open plan home and observe two backups although only one backup was run on host1
8. Open Web UI on host2, navigate to plans section, open plan home and observe two backups although only one backup was run on host2

Expected behavior
As of step 8 and 9 above:
8. Open Web UI on host1, navigate to plans section, open plan home and observe one backup of host1 (and maybe as a separate branch one backup of host2)
9. Open Web UI on host2, navigate to plans section, open plan home and observe one backup of host2 (and maybe as a separate branch one backup of host2)

The backups of different hosts should IMHO be visually clearly differentiated. I can imagine different solutions, e.g., tree view having ìnstallation-id`/host as one node, different sections per installation/host in plans section, enforcing distinctive plan-id's per repository (upgrade path?), ...

Platform Info

• OS and Architecture: Windows 10 x64
• Backrest Version: 1.6.2

Additional context

• The repository section in the Web UI shows a tree view, containing the installation-id/host as one level/node, thus allowing to differentiate between snapshots of different installations/hosts.
• In case reusing the same repository by different hosts/installations is discouraged, this should IMHO be clearly stated in the documentation, and better be enforced by code
• In case the plan-id needs to be distinctive within one repository, this should IMHO be clearly stated in the documentation, and better be enforced by code
• Thanks a lot for your work! Great to have a trustworthy backup solution available for non-IT-experts not using Linux.