feat: implement append mode to combine multiple outputs

[DaanRoet]

Totally vibe-coded but might be useful for our monorepo to avoid a little less spam

Example:

# First package
./pr-comments -token="$GITHUB_TOKEN" -pr="$PR_NUMBER" \
  -owner="owner" -repo="repo" \
  -body="<!-- package-publish-status -->
## :package: Package Publishing Status
> Packages published from this PR" \
  -body-includes="<!-- package-publish-status -->" \
  -append \
  -row-id="@myorg/package-a" \
  -columns="Package,Status,Version,Time" \
  -values="@myorg/package-a,:white_check_mark: success,\`@myorg/package-a@1.0.0-alpha.1\`,12:34:56"

# Second package
./pr-comments -token="$GITHUB_TOKEN" -pr="$PR_NUMBER" \
  -owner="owner" -repo="repo" \
  -body="<!-- package-publish-status -->
## :package: Package Publishing Status
> Packages published from this PR" \
  -body-includes="<!-- package-publish-status -->" \
  -append \
  -row-id="@myorg/package-b" \
  -columns="Package,Status,Version,Time" \
  -values="@myorg/package-b,:x: failure,-,12:35:10"

This will create or update a comment that looks like:

📦 Package Publishing Status

Packages published from this PR

Package	Status	Version	Time
@myorg/package-a	✅ success	@myorg/package-a@1.0.0-alpha.1	12:34:56
@myorg/package-b	❌ failure	-	12:35:10