fix(helper): search file error handling

[florian-hoenicke]

When running f = Flow.load_config('flow-index.yml'), I received the following error:
FileNotFoundError: [Errno 2] No such file or directory: '/Library/TeX/texbin/flow-index.yml'
This is because the file flow-index.yml did not exist. However, the error message tells me that the file does not exist in my LaTeX folder, which is weird.
It turned out that the current helper function takes the last path in the PATH variable as default. For sure, this is not intended.
I changed the implementation to fire an exception instead of taking the last path as default.

[codecov]

Codecov Report

Merging #1353 (fc845cb) into master (ac38ebf) will decrease coverage by 0.05%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1353      +/-   ##
==========================================
- Coverage   82.87%   82.81%   -0.06%     
==========================================
  Files         103      103              
  Lines        6746     6746              
==========================================
- Hits         5591     5587       -4     
- Misses       1155     1159       +4     

Impacted Files	Coverage Δ
jina/logging/sse.py	91.93% <0.00%> (-3.23%)	⬇️
jina/docker/hubio.py	64.85% <0.00%> (-0.86%)	⬇️
jina/peapods/grpc_asyncio.py	76.53% <0.00%> (+1.02%)	⬆️

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[cristianmtr]

But won't this affect performance? Recursively checking all these folders?

[JoanFM]

Performance is not an issue at this stage because this is all working at creation time and spin-up