How to prepare buildbot for major release

These are collected notes of the steps we've done during preparation of buildbot infrastructure for 21.02 release.

usign -G -c "Public usign key for 22.03 release builds" -s secret.key -p public.key

usign -F -p public.key
2f8b0b98e08306bf
 
mv public.key openwrt/keyring.git/usign/2f8b0b98e08306bf

Add usign secret.key to ansible/inventories/openwrt-secrets.yml:

vault_buildbot_usign_key_openwrt_22_03:

1. gpg: add OpenWrt 21.02 signing key
2. usign: add 21.02 release build pubkey

1. openwrt-keyring: add OpenWrt 21.02 GPG/usign keys
2. openwrt-keyring: make opkg use 22.03 usign key (NOTE: this needs to be done only in the release branch)

1. Add new key info to signatures page

1. inventory: add setup for 21.02 release

ansible-playbook --diff -i inventories/prod buildworker.yml --tags cfg,recreate-slave --limit fsf-02,fsf-04,osuosl-vm-03,osuosl-vm-04,truecz-01,truecz-02,buildmaster