Ensure we have enough people familiar with the codebase in
the owners

Test: None
Bug: None
Change-Id: Ie007c8a6c950f1d318fe5a699420b0ebe3a0f730

Test: build/make/tools/checkowners.py -c -v OWNERS
Change-Id: I1428fabcbac419ee9e9000f3fb8f9f97e187f3f3

* Owners are selected from top CL approvals or owners.
  They will be suggested to review/approve future CLs.
* OWNERS files are recognized by the new find-owners plugin, see .md files in
  https://gerrit.googlesource.com/plugins/find-owners/+/master/src/main/resources/Documentation/

Test: build/make/tools/checkowners.py -c -v OWNERS
Change-Id: I774442b315d32aff99574c48616b1a954719b95b