Merge accounts

[fherreazcue]

Adds methods and tests to be able to merge two accounts, transferring all the relevant associations without duplication.

Resolves #1666.

[stuzart]

A couple of minor comments on the main code, and the need to merge annotations the person has made.

Main concern is that the tests aren't robust enough, needs expanding a bit and more explicit checking. For this it is more important that the tests are really robust

[fbacall]

I did a search for belongs_to :user and found a few other associations:

The auth lookup tables will be too slow to update, but the various log tables are probably worth updating

[stuzart]

the auth lookup table should update automatically. rows will be removed when the user is destroyed (another case where we can enhance the delete_all). After it's merged I also plan to check what jobs get created, or whether it just needs a job firing at the end

[fbacall]

Maybe useful:
List of tables that reference user_id:

api_tokens
assay_auth_lookup
asset_doi_logs
collection_auth_lookup
data_file_auth_lookup
document_auth_lookup
event_auth_lookup
favourite_groups
favourites
file_template_auth_lookup
identities
investigation_auth_lookup
model_auth_lookup
moderatorships
oauth_sessions
placeholder_auth_lookup
presentation_auth_lookup
publication_auth_lookup
resource_publish_logs
sample_auth_lookup
saved_searches
sop_auth_lookup
strain_auth_lookup
study_auth_lookup
template_auth_lookup
workflow_auth_lookup

List of tables that reference person_id:

admin_defined_role_programmes
admin_defined_role_projects
disciplines_people
favourite_group_memberships
group_memberships
project_subscriptions
publication_authors
roles
subscriptions
users

[fherreazcue]

Just some notes on the comment above:
Person:
The roles, admin_defined_role_programmes, admin_defined_role_projects, group_memberships, subsriptions and users are already included.
For favourite_group_memberships, project_subscriptions and publication_authors, this needs to be added in the main merge method:

          merge_associations(other_person, 'favourite_group_memberships',
                             %i[favourite_group_id access_type], { person_id: id })
          merge_associations(other_person, 'project_subscriptions',
                             %i[project_id unsubscribed_types frequency], { person_id: id })
          merge_associations(other_person, 'publication_authors',
                             %i[first_name last_name publication_id author_index], { person_id: id })

with accompanying tests.
For disciplines_people I am unsure... the method person.disciplines bounces off the Disciplines table...

User:
Identities are already included.
For api_tokens, favourite_groups and oauth_sessions this can be added in the merge_user method:

        merge_user_associations(other_person, 'api_tokens',
                                %i[title], { user_id: user.id })
        merge_user_associations(other_person, 'favourite_groups',
                                %i[name], { user_id: user.id })
        merge_user_associations(other_person, 'oauth_sessions',
                                %i[provider], { user_id: user.id })

with accompanying tests.
For asset_doi_logs, favourites, moderatorships, resource_publish_logs and saved_searches I am not sure.