Scope and purpose

This PR will resolve #2344 when all dependent PRs are merged.
This PR resolves #3554 in itself.

Dependent PRs: #3553, #3557 (see dependency graph)

  graph LR;
      A(#3551: Base PR)
      B(#3553: Loading and subscription - merged)
      C(#3557: Dashboard search - merged)
      D(#3559: Export and import - merged)
      A-->B;
      B-->C;
      B-->D;

This PR adds support for sharing dashboards in NAV by modifying the account_dashboard table and adds a new account_dashboard_subscription table to hold account-dashboard joins.. A dashboard owner can set the dashboard as shared, which in turn will make it visible to other accounts in the follow-up PR.

This pull request

• Adds an is_shared property to the AccountDashboard model
• Adds new AccountDashboardSubscription to support account subscriptions on a dashboard
• Adds two new methods to the AccountDashboard model
  • can_edit(self, account): Used in views to determine if the request account has edit rights.
  • is_subscribed(self, account): Used in views to determine if the request account is subscribed to the dashboard.
• Adds a "Shared" section to the dashboard settings form
  • A shared dashboard shows a warning if the owner unchecks the shared checkbox, as this will remove any existing subscriptions.

Screenshots

A new Sharing form has been added to dashboard settings

This form shows a currently unshared dashboard.

Unsharing a dashboard

Shared dashboard form	Shared dashboard with "Share" unchecked

Contributor Checklist

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• Added a changelog fragment for towncrier
• Added/amended tests for new/changed code
• Added/changed documentation
• Linted/formatted the code with ruff, easiest by using pre-commit
• The first line of the commit message continues the sentence "If applied, this commit will ...", starts with a capital letter, does not end with punctuation and is 50 characters or less long. See https://cbea.ms/git-commit/
• This pull request is based on the correct upstream branch: For a patch/bugfix affecting the latest stable version, it should be based on that version's branch (<major>.<minor>.x). For a new feature or other additions, it should be based on master.
• If applicable: Created new issues if this PR does not fix the issue completely/there is further work to be done
• If this results in changes in the UI: Added screenshots of the before and after
• If this adds a new Python source code file: Added the boilerplate header to that file