Changes to metadata tags do not persist

[kiersten-stokes]

Describe the issue
Metadata tags do not persist when using 3.9.0rc0 and latest master branch. This is an issue both when creating a new tag (it disappears) or attempting to edit existing tags.

To Reproduce
Steps to reproduce the behavior:

1. Go to any metadata instance that has a tags field
2. Add a new tag to an instance, and 'Save & Close'
3. Note that tag doesn't appear in dropdown area where tags can be used as filters
4. Open same instance and see that tag doesn't show up in the edit page as well

Screenshots or log output
Console logs didn't seem to indicate anything out of the ordinary, nor do the debug logs (below).

Debug Log Output

[D 2022-06-01 12:31:17.662 ElyraApp] Loading metadata instance from cache: 'print'
[D 2022-06-01 12:31:17.663 ServerApp] MetadataHandler: Updating metadata instance 'print' in schemaspace 'code-snippets'...
[D 2022-06-01 12:31:17.663 ElyraApp] Loading metadata instance from cache: 'print'
[D 2022-06-01 12:31:17.666 ElyraApp] Renamed resource for instance 'print' to: '/Users/kierstenstokes/Library/Jupyter/metadata/code-snippets/print.json1654104677.6662002'
[D 2022-06-01 12:31:17.666 ElyraApp] Updated metadata instance: /Users/kierstenstokes/Library/Jupyter/metadata/code-snippets/print.json
[D 2022-06-01 12:31:17.666 ElyraApp] Loading metadata instance from: '/Users/kierstenstokes/Library/Jupyter/metadata/code-snippets/print.json'
[D 2022-06-01 12:31:17.667 ElyraApp] Loading metadata instance from cache: 'print'

Expected behavior
Changes to tags should persist

Deployment information
Describe what you've deployed and how:

• Elyra version: 3.9.0rc0 and latest master
• Installation source: PyPI for the rc