Allow passing already opened h5file to table loader

[maxnoe]

No description provided.

[codecov]

Codecov Report

Merging #1933 (e41b8b5) into master (0c628d7) will increase coverage by 0.00%.
The diff coverage is 95.45%.

@@           Coverage Diff           @@
##           master    #1933   +/-   ##
=======================================
  Coverage   92.09%   92.09%           
=======================================
  Files         189      189           
  Lines       14963    14984   +21     
=======================================
+ Hits        13780    13800   +20     
- Misses       1183     1184    +1     

Impacted Files	Coverage Δ
ctapipe/io/tests/test_table_loader.py	99.03% <90.90%> (-0.97%)	⬇️
ctapipe/io/tableloader.py	95.54% <100.00%> (+0.30%)	⬆️

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