Scope plugin operator extra links to their team in multi-team mode

[o-nikolas]

A team-scoped plugin's operator extra links were rendered on every task instance, so one team's links appeared on other teams' Dags and pointed users at systems they may have no access to.

Ownership is tracked per link class rather than per link name: link instances are unhashable and compare equal to each other, and a plugin link may deliberately share a name with an operator's own link, so a name key would make the operator's link look team-owned. A class registered by both a global and a team-scoped plugin stays global.

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