#2029 Generate a new job for importing nexus data from a file

This commits the result of
`bin/rails generate job import_nexus --queue import_nexus`

Testing that import_nexus jobs can be created and run:
* From `bin/rails c`, do `::ImportNexusJob.perform_later()`
* From an app shell, do `QUEUE=import_nexus rake jobs:workoff` - it should report a nexus_import job was run (if you `puts` some text from your job you should see the text in your console)

app/jobs/import_nexus_job.rb

@@ -0,0 +1,7 @@
+class ImportNexusJob < ApplicationJob
+  queue_as :import_nexus
+
+  def perform(*args)
+    # Do something later
+  end
+end

exe/delayed_job

@@ -2,4 +2,4 @@
 set -e
 
 cd /app
-exec chpst -u app env QUEUE=project_download,cached_map,dwca_export,coldp_export,basic_nomenclature_export,dwc_occurrence_index,dwca_build_index,import_dataset_import,import_dataset_stage,cache,query_batch_update /usr/bin/bundle exec rails jobs:work
+exec chpst -u app env QUEUE=project_download,cached_map,dwca_export,coldp_export,basic_nomenclature_export,dwc_occurrence_index,dwca_build_index,import_dataset_import,import_dataset_stage,cache,query_batch_update,import_nexus /usr/bin/bundle exec rails jobs:work

spec/jobs/import_nexus_job_spec.rb

@@ -0,0 +1,5 @@
+require 'rails_helper'
+
+RSpec.describe ImportNexusJob, type: :job do
+  pending "add some examples to (or delete) #{__FILE__}"
+end