Normalized schema additions

[pablojimpas]

Summary

References #395

Changes

• Introduce a new object for soil measurements.
• Add CO2 and light intensity properties to the air object.

Notes for Reviewers

• Some definitions are extracted, even though they are simple. I've done this because I think it's a good practice to have quantities and their context decoupled as much as possible, that way quantities can be reused as the schema evolves. This is problematic in some cases, for example, the atmospheric pressure has a range that may not be suitable for industrial valves, in this case, I think it makes more sense to maintain specific definitions inside each context.
• I've set the maximum of electrical conductivity based on the most conductive metal, silver. In practice, this is probably overkilled.
• I haven't set a closed range for the pH scale based on this: https://pubs.acs.org/doi/pdf/10.1021/ed083p1465. In practice, maybe it makes more sense to set it to [0, 14] since most sensors on the edge aren't able to measure very high or very low values https://pubs.acs.org/doi/abs/10.1021/ac60120a014. I haven't extracted the pH because it is ridiculously simple with these assumptions.
• I have only added a small batch of new measurements for now, please let me know if you prefer larger PRs, I leave this as a draft until we agree on the right size.

Release Notes

• Added support for soil measurements, CO2 and light intensity in the normalized payload schema.

[johanstokking]

Thanks! Few minor comments

I think it's useful to add a depth indicator to soil as well. It would be a value in centimeters.

Needs description fix

[pablojimpas]

Sorry, I haven't looked at GitHub in the last few days.
I've fixed that pH description I left off last time.

Other than figuring out the depth and elevation issue, what else is missing for this PR? Is this an acceptable number of additions to the schema, or should we proceed in larger batches?

[cBashTN]

Isn't the core idea of the normalizer to have standardized units? If yes, then why use cm instead of m?