Document microgrid component terminology for logical meters

[cwasicki]

The terminology of the microgrid components for the logical meters as described here should be documented: We could put it in the https://github.com/frequenz-floss/frequenz-sdk-python/wiki/Glossary, or it's own Wiki page for now. In the end I think it should be in the SDK documentation website (https://frequenz-floss.github.io/frequenz-sdk-python/v0.19/), but for now a Wiki page should be enough. (#250 (comment))

[leandro-lucarella-frequenz]

#318 was converted to a discussion, so we can keep discussing there.