[exporter/datadog] Upcoming breaking changes to configuration

[mx-psi]

We will be making some breaking changes to the Datadog exporter configuration for improving consistency and usability, including renaming some keys, reducing duplicated functionality and polishing the public Go API. All current end-user functionality will continue to be supported, either within the Datadog exporter or with the help of a suitable processor, language library or Collector option.

This issue intends to track the changes publicly so that we can help end-users in the transition and get feedback from them. Individual changes will have a dedicated issue with instructions on how to move to the new format. All changes will first have a deprecation period of at least one release where features/keys are documented as deprecated and a warning is logged to users. All deprecated settings or functionality will be removed at once in a future minor version to be determined.

I will keep this issue updated with the full list of issues tracking these changes. Comment on the individual issues if your feedback is related to one of them in particular.

Go API only changes

• [exporter/datadog] Move Config structs to main package and reduce API #8373

Go API + application behavior changes

• [exporter/datadog] Remove builtin support for environment variable detection #8396
• [exporter/datadog] Rename metrics::send_monotonic_counter to metrics::sums::cumulative_monotonic_mode #8489
• [exporter/datadog] Rename metrics::report_quantiles to metrics::summaries::mode #8845
• [exporter/datadog] Remove service setting #8781
• [exporter/datadog] Remove version setting #8783
• [exporter/datadog] Remove env setting #9016
• [exporter/datadog] Create host_metadata section to group related settings #9099

Tentative Calendar (only application behavior changes)

Version	Release date	Deprecations
v0.47.0	2022-03-17	automatic environment variable detection
v0.48.0	2022-03-31	metrics::send_monotonic_counter
v0.49.0	2022-04-20	env, service, version, tags send_metadata, use_resource_metadata
v0.50.0	2022-04-27	metrics::report_quantiles
v0.56.0	2022-07-20	Remove all deprecated settings

[mx-psi]

Updated description to reflect our new plan: remove all deprecated functionality together in one future minor version (TBD).

[mx-psi]

All steps are done.