Enh/convert mm to mmday when possible

[bzah]

Pull Request to resolve #xxx

• Unit tests cover the changes.
• These changes were tested on real data.
• The relevant documentation has been added or updated.
• A short description of the changes has been added to doc/source/references/release_notes.rst.

Describe the changes you made

• Bump icc version to 6.0.0 for upcoming release
• Remove ddNorth as it will be fixed by Enh/ecad wind indices #230
• Convert input data that are recognized as a precipitation amount into precipitation rate
  This is done by using the standard_name and the units attribute of the input dataset.

Related work on xclim: Ouranosinc/xclim#1206

[github-actions]

Report

File	Stmts	Miss	Cover	Missing
icclim
icclim_exceptions.py	7	1	86%	20
icclim_logger.py	85	29	66%	24, 43, 65, 70–95, 105, 111–142, 150–155
main.py	269	20	93%	118, 127, 402, 487, 513–514, 516–517, 519, 521–522, 524–525, 544–551, 688, 695, 699
utils.py	29	1	97%	20
icclim/generic_indices
cf_var_metadata.py	46	1	98%	19
generic_indicators.py	467	84	82%	57, 60, 77, 81, 85, 98, 104, 178, 217, 224, 348, 377, 659, 690, 696, 704, 723, 801, 821–827, 831, 861, 863, 928–929, 962–989, 1016–1037, 1053, 1062–1063, 1069–1099, 1105–1109, 1133
icclim/models
cf_calendar.py	35	1	97%	20
climate_variable.py	96	10	90%	97, 141, 152, 186, 192, 230, 234, 262–263, 300
frequency.py	176	11	94%	167–170, 314–316, 323, 401, 427, 432
index_group.py	34	1	97%	33
operator.py	29	1	97%	14
registry.py	33	1	97%	26
standard_index.py	30	2	93%	65, 69
threshold.py	389	26	93%	198, 225, 229, 277, 298, 305, 318–324, 329–340, 381, 386, 517, 586, 680, 883, 905, 911, 985, 988, 1086–1088
icclim/pre_processing
input_parsing.py	178	33	81%	41, 105, 110, 116, 125, 138, 167, 183, 197, 217, 225, 227, 236, 245, 263, 277–285, 294–309, 331
rechunk.py	86	2	98%	38, 132
TOTAL	2382	224	91%

Test results

Tests	Skipped	Failures	Errors	Time
181	0 💤	0 ❌	0 🔥	2m 5s ⏱️