CODEOWNERS: remove core set of maintainers from CODEOWNERS (#5769)

Previously, CODEOWNERS were introduced to split PRs across the following
groups:

* @grafana/grafana-agent-core-maintainers
* @grafana/grafana-agent-signals-maintainers
* @grafana/grafana-agent-operator-maintainers
* @grafana/grafana-agent-infrastructure-maintainers

However, membership of these groups is broad, with a lot of overlap.
Furthermore, high PR volume meant that members of these groups had
a high amount of notification noise, which makes it difficult to track
what work an individual is actually responsible for.

This commit removes these four groups from CODEOWNERS, and shifts PR
tracking to GitHub project boards. This reduces the notification noise
of group members, and group members to more selectively choose what PRs
they want to get involved in.

CODEOWNERS

@@ -1,25 +1,10 @@
-# The following groups are used to refer to a changing set of users:
+# The CODEOWNERS file is used to define ownership of individuals or teams
+# outside of the core set of Grafana Agent maintainers.
 #
-# * @grafana/grafana-agent-core-maintainers: maintainers of type/core issues.
-# * @grafana/grafana-agent-signals-maintainers: maintainers of type/signals issues.
-# * @grafana/grafana-agent-operator-maintainers: maintainers of type/operator issues.
-# * @grafana/grafana-agent-infrastructure-maintainers: maintainers of type/infrastructure issues.
-#
-# Other users may be listed explicitly if maintainership does not fall into one
-# of the above groups.
-
-# The default owners for everything in the repo. Unless a later match takes
-# precedence, these owners are requested for review whenever someone opens a
-# pull request.
-* @grafana/grafana-agent-core-maintainers
-
-# Some directories have shared ownership with the respective owners of the
-# specific code for the PR being opened, so there's no CODEOWNERS.
-/CHANGELOG.md
-/component/all
-
-# Binaries:
-/cmd/grafana-agent-operator/  @grafana/grafana-agent-operator-maintainers
+# If a directory is not listed here, it is assumed to be owned by the
+# @grafana/grafana-agent-maintainers; they are not explicitly listed as
+# CODEOWNERS as a GitHub project board is used instead for PR tracking, which
+# helps reduce notification noise of the members of that team.
 
 # `make docs` procedure and related workflows are owned by @jdbaldry.
 /.github/workflows/publish-technical-documentation-next.yml    @jdbaldry
@@ -30,25 +15,7 @@
 /docs/variables.mk                                             @jdbaldry
 
 # Documentation:
-/docs/sources/  @clayton-cornell
+/docs/sources/ @clayton-cornell
 
 # Components:
-/component/discovery/               @grafana/grafana-agent-infrastructure-maintainers
-/component/local/                   @grafana/grafana-agent-infrastructure-maintainers
-/component/loki/                    @grafana/grafana-agent-signals-maintainers
-/component/loki/source/podlogs/     @grafana/grafana-agent-infrastructure-maintainers
-/component/mimir/rules/kubernetes/  @grafana/grafana-agent-infrastructure-maintainers
-/component/otelcol/                 @grafana/grafana-agent-signals-maintainers
-/component/prometheus/              @grafana/grafana-agent-signals-maintainers
-/component/prometheus/exporter/     @grafana/grafana-agent-infrastructure-maintainers
-/component/prometheus/operator/     @grafana/grafana-agent-operator-maintainers
-/component/pyroscope/               @grafana/grafana-agent-profiling-maintainers
-/component/remote/                  @grafana/grafana-agent-infrastructure-maintainers
-
-# Static mode packages:
-/pkg/integrations/  @grafana/grafana-agent-infrastructure-maintainers
-/pkg/logs/          @grafana/grafana-agent-signals-maintainers
-/pkg/metrics/       @grafana/grafana-agent-signals-maintainers
-/pkg/mimir/client/  @grafana/grafana-agent-infrastructure-maintainers
-/pkg/operator/      @grafana/grafana-agent-operator-maintainers
-/pkg/traces/        @grafana/grafana-agent-signals-maintainers
+/component/pyroscope/ @grafana/grafana-agent-profiling-maintainers