Rename Experimental to Development according to OTEP 0232

[tigrannajaryan]

Resolves #4051

OTEP 0232 brought new stability definitions.

The impact on this repository is that we need to rename "Experimental" to "Development". All other existing statuses remain unchanged.

Note: OTEP 0232 also introduces other levels, such as Alpha, Beta, etc. We will need to decide separately if we want to start using these levels in this repository.

[tigrannajaryan]

@open-telemetry/configuration-maintainers are you OK if we also rename OTEL_EXPERIMENTAL_CONFIG_FILE to OTEL_DEVELOPMENT_CONFIG_FILE? This is the only remaining usage of word "experimental" in the repo.

[MrAlias]

@open-telemetry/configuration-maintainers are you OK if we also rename OTEL_EXPERIMENTAL_CONFIG_FILE to OTEL_DEVELOPMENT_CONFIG_FILE? This is the only remaining usage of word "experimental" in the repo.

I think this can be left as is. The OTEP about maturity levels doesn't cover environment variable names, and changing that would only cause unnecessary disruption.

That key has a limited life. I think we can just let it exist that way until it is replaced with a stable version.

[tigrannajaryan]

@open-telemetry/configuration-maintainers are you OK if we also rename OTEL_EXPERIMENTAL_CONFIG_FILE to OTEL_DEVELOPMENT_CONFIG_FILE? This is the only remaining usage of word "experimental" in the repo.

I think this can be left as is. The OTEP about maturity levels doesn't cover environment variable names, and changing that would only cause unnecessary disruption.

That key has a limited life. I think we can just let it exist that way until it is replaced with a stable version.

SGTM. I am going to keep it as is.

[tigrannajaryan]

@chalin thanks for review. I capitalized Development everywhere and got rid of "in-" prefix where possible based on your suggestions. I left out a couple of your suggestion since they are a bit more extensive editing that I think is best done in a separate PR.