[dashboard] Add chart you are not owner of to dashboard

[zuzana-vej]

Motivation / Problem to Solve

Sometimes users would like to add chart they are not owner of to their dashboard. Related feature request: apache/superset#12275

Proposed Functionality

User should be able to add a chart they are no owner of into the dashboard.
User research and discussions will be necessary to determine whether this feature should be implemented and how.

[zuzana-vej]

Considerations / Discussion points:

• Even list of charts which user owns / co-owns is long, and seeing all charts would be overwhelming, so there will need to be distinction (my charts vs. other charts).
• Chart owner whose chart was added into dashboard might need to know about it (e.g. so that they don't delete it) - probably ability to see "all dashboard this chart is part of" on chart Explore or in chart properties, consider also getting notification to chart owners. Should chart owner just be notified? Should they "approve"?
• This feature might not be welcome by everyone, so probably should be configurable whether an organization will enable this or on.
• It would be good overall to get inputs from various users on whether they would actually use this functionality.
• Alternative to this is more team based approach to chart ownership - and if that is implemented this feature could be obsolete. If instead of people, charts are owned by a team or multiple teams, and anyone from the team can add those charts onto the dashboard, if certain organizations wants anyone to add any chart, they will just setup their chart ownership in that way.