Docs: Single ClusterExtension ownership concept

[joelanford]

#736 has become a documentation-only epic, so this issue tracks authoring that doc. From the description:

For v1.0.0 it was decided that utilizing the underlying Helm management when concurrent reconciliations is set to a value of 1 is sufficient. While the underlying implementation details may change to prevent race conditions when scaling concurrent reconciliations > 1, the behavior that no two ClusterExtensions should be able to manage the same underlying objects needs to be documented.

Documentation should be contributed to the docs/drafts/ directory

[LalatenduMohanty]

#1258 is under review

[everettraven]

#1258 merged