* Add Device (Mobile) and OS Version Resource Semantic Attributes
* Added OS Name (iOS) and OS Version (14.4) to `os`.
* Added Device Identifier and Model Identifier to a newly created `device` group.
* Have consistent formatting for semantic convention enums
Currently, semantic convention enum values are not consistent.
For example, os.type values are all capitals whereas
cloud.infrastructure_service values are underscored lowercase.
This change improves the inconsistencies.
We also expect language implementations to autogenerate code
from enum values. Each language has their own conventions for
constant variable identifiers and we expect the consistent
formatting is going to help the language implementors.
Fixes#1519.
Liudmila Molkova