Select preferred units of measurement (inches/metric)

[DerekCaelin]

While most data collectors are comfortable working in the metric system, some users prefer to use inches and feet, rather than centimeters. Allow users to select their preferred units of measurement.

Requested during a usability test.

Relevant for US/Global Soil ID and monitoring app.

References

Product Spec

Designs

TBD Slim MVP design (to be updated)

Process

### Issues
- [ ] https://github.com/techmatters/terraso-product/issues/952
- [ ] https://github.com/techmatters/terraso-product/issues/1003
- [ ] Team Reviews design
- [ ] https://github.com/techmatters/terraso-mobile-client/issues/1976
- [ ] QA
- [ ] Translation
- [ ] Usability testing
- [ ] Web Documentation

Acceptance Criteria

• [ ] As a contributor/site owner, I can choose which units of measurement I want to see while using the app, so I can think in the units in which I am most comfortable
• [ ] As a manager of a project, I want to choose which units of measurement to assign to others while using the app, so I can standardize our data collection in the units that make the most sense to me

[DerekCaelin]

A user (Rancher Stewardship Alliance) requested this in a usability test. "I know meters are real, but is there any way it could be in feet?"