Migrating objects between spaces

[markwalkom]

Describe the feature: We should be able to leverage _reindex to move things between spaces via the UI.

Describe a specific use case for the feature:
Rather than doing the export > change space in Kibana > import route, a reindex should be able to do the same thing for the user.

[elasticmachine]

Pinging @elastic/kibana-security

[markwalkom]

An example - I have a bunch of spaces for some personal data and they all have dashboards for each space. I also want to have a space that I can pull together some of the visualisations from the other spaces to make a meta-dashboard.

[legrego]

While a _reindex would enable this on a per-object basis, we are interested in supporting an even friendlier experience. When moving objects between spaces, we want to be able to move all related objects as well. For example, moving a dashboard should also move (or copy) associated visualizations, index patterns, etc to the target space, without the user having to manually do this.

We'd like to leverage #27210 to facilitate this in the future. Once saved object relationships are well-defined, we will be able to design a more curated experience for moving objects (and related objects) between spaces.

[kobelb]

This will be addressed by #37286