(minor) bug report: Incorrect line numbers in GRDC metadata reader

[andrevdv]

In def _grdc_metadata_reader the line numbers used to extract metadata from .txt are off by one:

ewatercycle/src/ewatercycle/observation/grdc.py

Lines 354 to 361 in ce00996

	attribute_grdc["dataSetContent"] = str(all_lines[20].split(":")[1].strip())
	except (IndexError, ValueError):
	attribute_grdc["dataSetContent"] = "NA"
	try:
	attribute_grdc["units"] = str(all_lines[22].split(":")[1].strip())
	except (IndexError, ValueError):
	attribute_grdc["units"] = "NA"

• dataSetContent is currently read from index 20, but should be 21 to read line 22 in the .txt
• units is currently read from index 22, but should be 23 to read line 24 in the .txt

Additionally, the "units" attribute is not currently used, units are currently hardcoded in the description when creating the xarray object

Proposed fix:

• Update the indices to 21 and 23.
• Optionally remove or repurpose the unused "units" attribute to avoid confusion.

PS: As mentioned to @RolfHut, I’m currently working on extending the GRDC station reader to also handle stations with monthly data instead of daily. I could bundle these bugfixes with that, if preferred.

[MarkMelotto]

@andrevdv thank you very much :)
I have fixed the bug and await the approval of @RolfHut

for the "units" part, if you can fix this together with what you are working on that would be amazing!