VAULT-6818 - Restrict ability to merge entities with mount-accessor-c…

…onflicting aliases unless one is explicitly chosen to be kept (#16539)

* VAULT-6818 delete unmerged entity aliases instead of orphaning them

* VAULT-6818 Prevent merge with clashing aliases, allow for resolution of clashing entity aliases

* VAULT-6818 Small updates

* VAULT-6818 Restrict to only one clash merge at once

* VAULT-6818 changelog

* VAULT-6818 use strutil package instead of slices

* VAULT-6818 Update variable names for clarity

* VAULT-6818 Update test

* VAULT-6818 update error message

* VAULT-6818 Use helper method

* VAULT-6818 validate entityIds

* VAULT-6818 group imports better

* VAULT-6818 use change instead of bug

* VAULT-6818 use multierror instead of custom struct

* VAULT-6818 Use multierror properly

* VAULT-6818 Small refactor based on feedback

changelog/16539.txt

@@ -0,0 +1,3 @@
+```release-note:change
+core/entities: Fixed stranding of aliases upon entity merge, and require explicit selection of which aliases should be kept when some must be deleted
+```