Fix creating tags within sessionless context

xref: https://github.com/galaxyproject/galaxy/issues/13551, fixes
```
galaxy.jobs ERROR 2022-03-15 00:21:29,515 [pN:main,p:2180,tN:LocalRunner.work_thread-3] problem importing job outputs. stdout [] stderr [
Traceback (most recent call last):
  File "metadata/set.py", line 1, in <module>
    from galaxy_ext.metadata.set_metadata import set_metadata; set_metadata()
  File "/home/runner/work/galaxy/galaxy/galaxy root/lib/galaxy/metadata/set_metadata.py", line 121, in set_metadata
    set_metadata_portable()
  File "/home/runner/work/galaxy/galaxy/galaxy root/lib/galaxy/metadata/set_metadata.py", line 291, in set_metadata_portable
    collect_dynamic_outputs(job_context, output_collections)
  File "/home/runner/work/galaxy/galaxy/galaxy root/lib/galaxy/job_execution/output_collect.py", line 147, in collect_dynamic_outputs
    persist_elements_to_hdca(job_context, elements, hdca, collector=DEFAULT_DATASET_COLLECTOR)
  File "/home/runner/work/galaxy/galaxy/galaxy root/lib/galaxy/model/store/discover.py", line 719, in persist_elements_to_hdca
    filenames,
  File "/home/runner/work/galaxy/galaxy/galaxy root/lib/galaxy/model/store/discover.py", line 292, in populate_collection_elements
    final_job_state=final_job_state,
  File "/home/runner/work/galaxy/galaxy/galaxy root/lib/galaxy/model/store/discover.py", line 354, in _populate_elements
    self.add_tags_to_datasets(datasets=element_datasets["datasets"], tag_lists=element_datasets["tag_lists"])
  File "/home/runner/work/galaxy/galaxy/galaxy root/lib/galaxy/model/store/discover.py", line 576, in add_tags_to_datasets
    self.tag_handler.add_tags_from_list(user, dataset, tags, flush=False)
  File "/home/runner/work/galaxy/galaxy/galaxy root/lib/galaxy/model/tags.py", line 61, in add_tags_from_list
    return self.set_tags_from_list(user, item, new_tags_set, flush=flush)
  File "/home/runner/work/galaxy/galaxy/galaxy root/lib/galaxy/model/tags.py", line 75, in set_tags_from_list
    self.apply_item_tags(user, item, unicodify(new_tags_str, "utf-8"), flush=flush)
  File "/home/runner/work/galaxy/galaxy/galaxy root/lib/galaxy/model/tags.py", line 207, in apply_item_tags
    self.apply_item_tag(user, item, name, value, flush=flush)
  File "/home/runner/work/galaxy/galaxy/galaxy root/lib/galaxy/model/tags.py", line 179, in apply_item_tag
    tag = self._get_or_create_tag(lc_name)
  File "/home/runner/work/galaxy/galaxy/galaxy root/lib/galaxy/model/tags.py", line 281, in _get_or_create_tag
    tag = self._create_tag(scrubbed_tag_str)
  File "/home/runner/work/galaxy/galaxy/galaxy root/lib/galaxy/model/tags.py", line 246, in _create_tag
    tag = self._create_tag_instance(tag_name)
  File "/home/runner/work/galaxy/galaxy/galaxy root/lib/galaxy/model/tags.py", line 428, in _create_tag_instance
    tag = super()._create_tag_instance(tag_name)
  File "/home/runner/work/galaxy/galaxy/galaxy root/lib/galaxy/model/tags.py", line 259, in _create_tag_instance
    Session = sessionmaker(self.sa_session.bind)
AttributeError: 'NoneType' object has no attribute 'bind'
]
Traceback (most recent call last):
  File "/home/runner/work/galaxy/galaxy/galaxy root/lib/galaxy/jobs/__init__.py", line 1828, in finish
    import_model_store.perform_import(history=job.history, job=job)
  File "/home/runner/work/galaxy/galaxy/galaxy root/lib/galaxy/model/store/__init__.py", line 209, in perform_import
    datasets_attrs = self.datasets_properties()
  File "/home/runner/work/galaxy/galaxy/galaxy root/lib/galaxy/model/store/__init__.py", line 930, in datasets_properties
    datasets_attrs = load(open(datasets_attrs_file_name))
FileNotFoundError: [Errno 2] No such file or directory: '/tmp/tmp19s6x278/tmpt0rr8vmw/tmp2mjq6ysx/database/job_working_directory1/000/7/metadata/outputs_populated/datasets_attrs.txt'
galaxy.jobs.runners ERROR 2022-03-15 00:21:29,516 [pN:main,p:2180,tN:LocalRunner.work_thread-3] (7/) Job wrapper finish method failed
Traceback (most recent call last):
  File "/home/runner/work/galaxy/galaxy/galaxy root/lib/galaxy/jobs/runners/__init__.py", line 594, in _finish_or_resubmit_job
    job_stderr=job_stderr,
  File "/home/runner/work/galaxy/galaxy/galaxy root/lib/galaxy/jobs/__init__.py", line 1828, in finish
    import_model_store.perform_import(history=job.history, job=job)
  File "/home/runner/work/galaxy/galaxy/galaxy root/lib/galaxy/model/store/__init__.py", line 209, in perform_import
    datasets_attrs = self.datasets_properties()
  File "/home/runner/work/galaxy/galaxy/galaxy root/lib/galaxy/model/store/__init__.py", line 930, in datasets_properties
    datasets_attrs = load(open(datasets_attrs_file_name))
FileNotFoundError: [Errno 2] No such file or directory: '/tmp/tmp19s6x278/tmpt0rr8vmw/tmp2mjq6ysx/database/job_working_directory1/000/7/metadata/outputs_populated/datasets_attrs.txt'
```