Grower account duplicate detection, suggestion and merger

Much like the contacts.google.com "Merge and fix" function it would be great to have a list of planters displayed in groups that share the same information such as device_id, telephone number and at least one name (exact parameters to be discussed). The grouped planter info would then be merged by an admin into one only when 100% sure about the duplicate account. The trees would also have to be reallocated to the new merged planter id. A great task for new developers.

No files, tests, or entry points are named in the issue, so first map the admin panel's planter-management flow and the existing account and tree APIs. Clarify the matching fields and merge safeguards with maintainers; done means admins can review grouped duplicate planters, merge a confirmed duplicate, and preserve all trees under the resulting planter.

Written by the indexing model from the issue text.