feat: add --reviewers-from-owners flag to auto-discover reviewers from OWNERS files

[qinqon]

Summary

Add a flag that automatically discovers reviewers and approvers from the repository's OWNERS and OWNERS_ALIASES files (Prow/Kubernetes-style) and adds them to the reviewers whitelist. This avoids manually listing every reviewer in the systemd unit or CLI flags.

Problem

Currently, to respond to reviews from project maintainers, you must manually list every username in --reviewers:

--reviewers=coderabbitai[bot],nunnatsa,orenc1,awels,akalenyu,enxebre,csrwng,sjenning,muraee,bryan-cox,cblecker,jparrill,devguyio,sdminonne,clebs,Nirshal

This is fragile — when team membership changes, the flag must be updated manually. It also requires knowing the OWNERS file structure upfront.

Solution

Add a --reviewers-from-owners flag that reads the OWNERS and OWNERS_ALIASES files from the repo and automatically adds all listed reviewers and approvers to the whitelist.

New flag

Flag	Env var	Default	Description
--reviewers-from-owners	OOMPA_REVIEWERS_FROM_OWNERS	false	Auto-discover reviewers from OWNERS/OWNERS_ALIASES files

Usage

# Auto-discover all reviewers/approvers from OWNERS files
oompa --repo openshift/hypershift --watch-prs 8365 \
  --reviewers-from-owners \
  --reviewers=coderabbitai[bot]  # can still add extra reviewers (bots, etc.)

# The two lists are merged — OWNERS reviewers + explicit --reviewers

Implementation

1. Add ReviewersFromOwners bool to Config struct
2. Add --reviewers-from-owners flag in main.go
3. After cloning the repo (in EnsureRepoCloned), if the flag is set:
   • Read OWNERS file from the repo root (YAML format)
   • Read OWNERS_ALIASES file if it exists (resolves group names to usernames)
   • Extract all reviewers and approvers entries, resolving aliases
   • Merge with any explicit --reviewers list
4. Support nested OWNERS files — for PRs that touch specific directories, also read OWNERS files from those directories (e.g. test/e2e/OWNERS)
5. Support the filters format used by some projects (regex-based path matching with per-path reviewers/approvers)

OWNERS file formats to support

Standard format:

approvers:
  - user1
  - user2
reviewers:
  - user3
  - user4

With aliases:

approvers:
  - team-approvers  # resolved via OWNERS_ALIASES
reviewers:
  - team-reviewers

OWNERS_ALIASES:

aliases:
  team-approvers:
    - user1
    - user2
  team-reviewers:
    - user3
    - user4

Filtered format (openshift/hypershift style):

filters:
  ".*":
    approvers:
      - core-approvers
    reviewers:
      - core-reviewers
  ".*kubevirt.*":
    approvers:
      - kubevirt-approvers
    reviewers:
      - kubevirt-reviewers

Open questions

• Should oompa only load reviewers matching the PR's changed files (path-filtered), or load all reviewers from the repo?
• Should OWNERS discovery happen once at startup or refresh periodically?
• Should there be a --reviewers-from-owners-path to specify which OWNERS file to read (for repos with non-standard locations)?

Acceptance criteria

• --reviewers-from-owners loads reviewers and approvers from OWNERS files
• OWNERS_ALIASES are resolved correctly
• Explicit --reviewers are merged with OWNERS-discovered reviewers
• Bot reviewers (e.g. coderabbitai[bot]) still work via explicit --reviewers
• Works with standard, aliased, and filtered OWNERS formats
• All existing tests pass
• New tests for OWNERS parsing