Add option single_ob to HDF5Merger for merging chunks of the same ob

[maxnoe]

Needed for merging of observations that are stored in multiple chunks into one final file for the OB.

TODO:

• [ ] Add test

[kosack]

Is an option really needed for this? I would think the default behavior should just be updated to not duplicate an OB if it already exists.

[maxnoe]

Is an option really needed for this? I would think the default behavior should just be updated to not duplicate an OB if it already exists.

That could be done, yes. Depends a bit on the use case, e.g. we might want to check for uniqueness of obs_id and error out if not single_ob to prevent people from merging the same file twice or merging two simulation files that are different but have the same run number

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (4a45dcd) 92.46% compared to head (4c334bf) 92.46%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #2436 +/- ## ======================================= Coverage 92.46% 92.46% ======================================= Files 234 234 Lines 19868 19872 +4 ======================================= + Hits 18370 18374 +4 Misses 1498 1498 ```

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