Don't look if ADF output in cupid-webpage unless cupid-diagnostics ran the atm notebooks

[mnlevy1981]

Describe the bug
When testing #159, I ran

$ cupid-diagnostics --land
$ cupid-webpage

and got

Traceback (most recent call last):
  File "${CONDA_ENVS}/cupid-infrastructure/bin/cupid-webpage", line 8, in <module>
    sys.exit(build())
             ^^^^^^^
  File "${CONDA_ENVS}/cupid-infrastructure/lib/python3.11/site-packages/click/core.py", line 1157, in __call__
    return self.main(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "${CONDA_ENVS}/cupid-infrastructure/lib/python3.11/site-packages/click/core.py", line 1078, in main
    rv = self.invoke(ctx)
         ^^^^^^^^^^^^^^^^
  File "${CONDA_ENVS}/cupid-infrastructure/lib/python3.11/site-packages/click/core.py", line 1434, in invoke
    return ctx.invoke(self.callback, **ctx.params)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "${CONDA_ENVS}/cupid-infrastructure/lib/python3.11/site-packages/click/core.py", line 783, in invoke
    return __callback(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "${CUPID_ROOT}/cupid/cupid_webpage.py", line 57, in build
    shutil.copytree(
  File "${CONDA_ENVS}/cupid-infrastructure/lib/python3.11/shutil.py", line 559, in copytree
    with os.scandir(src) as itr:
         ^^^^^^^^^^^^^^^
FileNotFoundError: [Errno 2] No such file or directory: './ADF_output'

To Reproduce
Run cupid-diagnostics for the key_metrics example on a subset of components that does not include the atmosphere, then run cupid-webpage

Expected behavior
Only try to copy output from the ADF if it exists (or maybe if we expect it to exist?)