Add app-template example

[blythed]

Description

Related Issues

Checklist

• Is this code covered by new or existing unit tests or integration tests?
• Did you run make test successfully?
• Do new classes, functions, methods and parameters all have docstrings?
• Were existing docstrings updated, if necessary?
• Was external documentation updated, if necessary?

Additional Notes or Comments

[codecov-commenter]

Codecov Report

Attention: 34 lines in your changes are missing coverage. Please review.

Comparison is base (34830a7) 80.33% compared to head (ea9aeaa) 67.80%.
Report is 144 commits behind head on main.

Files	Patch %	Lines
superduperdb/backends/dask/compute.py	47.05%	18 Missing ⚠️
superduperdb/backends/base/compute.py	68.96%	9 Missing ⚠️
superduperdb/backends/base/query.py	85.71%	3 Missing ⚠️
superduperdb/backends/base/metadata.py	75.00%	2 Missing ⚠️
superduperdb/backends/base/artifact.py	80.00%	1 Missing ⚠️
superduperdb/backends/base/data_backend.py	80.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #1425       +/-   ##
===========================================
- Coverage   80.33%   67.80%   -12.54%     
===========================================
  Files          95      103        +8     
  Lines        6602     7340      +738     
===========================================
- Hits         5304     4977      -327     
- Misses       1298     2363     +1065     

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