Add a project changelog

[MrAlias]

Now that we are making releases we need a way to track and communicate to users changes we make.

• Decide on a changelog format
• Decide on a changelog policy
• Add tooling to enforce any required policy actions

[MrAlias]

Option 1

Follow go.opentelemetry.io/otel and use the keep a changelog format.

Option 2

Follow go.opentelemetry.io/collector and use the bespoke "OTel" changelog and its utility.

[MrAlias]

• Add tooling to enforce any required policy actions

We should add a policy that requires any user-facing changes (API, behavior, performance) to require a changelog. We should follow other repositories and built a CI check to ensure this is enforced.

Similarly, we should also provide exceptions for this requirements when the change is trivial, internal, or a non-user-facing task (i.e. dependencies, CI, minor edits).

[MrAlias]

Another thing we could do is split out the "What's changed" sections.

https://docs.github.com/en/repositories/releasing-projects-on-github/automatically-generated-release-notes#configuring-automatically-generated-release-notes