OPENTELEMETRY_COLLECTOR_CONFIG_FILE env var name is ambiguous

[garysassano]

The ADOT collector supports the following types of confmap providers: file, env, yaml, http, https, and s3.

However, the environment variable name OPENTELEMETRY_COLLECTOR_CONFIG_FILE might misleadingly suggest that it is only applicable to the file provider. A more generic name, such as OPENTELEMETRY_COLLECTOR_CONFIG, would be more appropriate.

Additionally, I find the documentation somewhat inconsistent. It initially states that the config should be provided in the <scheme>:<value> format but later shows examples where specifying the scheme is optional in certain cases:

To address this inconsistency, I recommend making it mandatory to define the scheme type explicitly.