Clearing cache event, even once, creates performance issues for Change Shared Entity Owner script

The Change Dashboard or Filter Ownership script can sometimes cause performance issues in very large instances running JIRA DataCenter. This is because we publish a ClearCacheEvent in order to make sure that, after the Dashboard and/or filters have changed ownership. While this doesn't typically cause problems, it can create issues when multiplied out across multiple nodes, since cache replication can take quite a bit of time.

We need to see if we can get by with PortalPageService#updatePortalPage and SearchRequestService#updateFilter; Atlassian recommends those to publishing a global clear cache event, and says we should submit a bug request if they aren't sufficient.