* 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.
* Avoid using "infrastructure" terminology for all cloud
Infrastructure in cloud has a specific connotation for concepts
explained in Infrastructure-as-a-Service (IaaS). Avoid this
termilogy because it's exclusive of some other services/platforms
that is represented by the "cloud" namespace.
Renaming "infrastructure_service" to "service" also due to the new
key length limits we are considering and infrastructure_service is
a lengthy choice.
Christian Neumüller