Manage dashboard access rights per Group and per User

[MichaelRodriguesOficial]

Update to better manage access to the dashboards.

Checklist before requesting a review

• I have performed a self-review of my code.
• I have added tests (when available) that prove my fix is effective or that my feature works.
• I have updated the CHANGELOG with a short functional description of the fix or new feature.
• This change requires a documentation update.

Description

Currently, dashboard access can only be granted per Profile. This PR adds the ability to also grant (or deny) access per Group and per User, using the same rights mechanism (Profile::dropdownRight) already used for profiles.

• Adds a new PluginMetabaseItemright class, mirroring PluginMetabaseProfileright, storing rights keyed by itemtype (Group or User) + items_id + dashboard_uuid.
• Adds a new tab ("Metabase") on the Group and User forms, gated by the existing group/user UPDATE rights, to manage dashboard access for that group/user.
• Access rights are now additive: a dashboard is shown on Central if the user's profile, any of their groups, or the user themselves has been granted READ access.
• No changes to the existing profile-based rights: they keep working exactly as before, this is purely additive.

I did not add automated tests since the plugin doesn't currently have a test suite in place.

Screenshots:

[Rom1-B]

Several errors in the CI

[Rom1-B]

Please correct the CI issues before requesting another review.