Opentelemetry-specification: Changelog entries create merge conflicts

[Oberon00]

The changelog entries we have at the moment create merge conflicts for every PR that touches the changelog file. I have seen a neat solution to this in the pytest repository where each changelog entry is placed in its own file in a changelog subdirectory and before a release, they run a tool that collects all entries into a single text. See https://github.com/pytest-dev/pytest/blob/master/CONTRIBUTING.rst#preparing-pull-requests

[tigrannajaryan]

I think this is a nice-to-have, not a must-have for 1.0 GA. I suggest to remove release:required-for-ga label.