Allow to share to space from tag management section

[pgayvallet]

extracted from #74571

This issue is here to discuss about the addition of a 'share to space' action from the tag management section, that would allow to share a tag and all the objects that are currently assigned to it to another space(s).

For the MVP, we decided to keep this feature in the SO management section, as it can already be achieved by filtering by tag and then sharing the objects to space.

Do we even that that, or are we good just keeping this in SO management?

cc @kobelb

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Edit 2021-03-31 by @jportner :

Sharing Saved Objects, Phase 3 (#67380) will add support for sharing an object and all of its "child relatives" (outbound references).

As a follow-on to that enhancement, we should add a variant of the flyout for the Tags Management page that allows you to share tags and all of their "parent relatives" (inbound references). Mockup:

[elasticmachine]

Pinging @elastic/kibana-core (Team:Core)

[kobelb]

FWIW, I think it's conceptually fine for us to add the ability to share a tag and all of the tagged saved-objects from tag management.