Dev barra2 pipeline

[christianstassen]

This introduces a notebook showing how to create a pipeline for BARRA-R2 and ERA5.

I also added a bunch of new Transforms, which introduce arithmetics (add, subtract, multiply and divide) and a new Operation to round valid time steps.

The transforms are part of the notebook, I thought it might be helpful for other to see how to create their own but, I also added them to the PET source code.

All changes have been tested by me in the notebook, by pytest, and I have run the black tool.

[coveralls]

Pull Request Test Coverage Report for Build 18769161211

Details

• 35 of 125 (28.0%) changed or added relevant lines in 3 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.3%) to 61.023%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
packages/pipeline/src/pyearthtools/pipeline/operations/xarray/round_time.py	8	26	30.77%
packages/data/src/pyearthtools/data/transforms/arithmetic.py	26	98	26.53%

Totals
Change from base Build 18765016601:	-0.3%
Covered Lines:	9592
Relevant Lines:	15297

---

💛 - Coveralls