Add bootapi-images repository

bootapi-images builds the AlmaLinux node rootfs tarballs that bootapi's
image-based provisioning (liveimg) unpacks, and on a v* tag publishes
almalinux9-node-<ver>.tar.zst to the artifactapi rootfs-images local repo. Split
out of bootapi-templates so that repo stays templates-only.

Modeled on the bootapi-templates entry: public, squash, delete-branch-after-merge,
main protection requiring the pre-commit + lint Woodpecker checks and benvin
approval.

Claude-Session: https://claude.ai/code/session_015ur3i7D2azsMAWTSVABApv

config/git.unkin.net/unkin/repository/bootapi-images.yaml

@@ -0,0 +1,13 @@
+description: "Builds AlmaLinux node rootfs tarballs for bootapi image-based provisioning; on v* tag publishes almalinux9-node-<ver>.tar.zst to the artifactapi rootfs-images repo."
+private: false
+default_branch: "main"
+default_delete_branch_after_merge: true
+default_merge_style: "squash"
+branch_protection:
+  - rule_name: "main"
+    enable_push: false
+    status_check_contexts:
+      - "ci/woodpecker/pr/pre-commit"
+      - "ci/woodpecker/pr/lint"
+    approval_whitelist_users:
+      - "benvin"