Add OpenStack provider support

[mendarb]

Summary

• Add OpenStack as a new cloud provider for the Woodpecker CI autoscaler using the gophercloud SDK (v2)
• Implement the Provider interface (DeployAgent, RemoveAgent, ListDeployedAgentNames) via OpenStack Compute (Nova) API
• Support standard OpenStack authentication (Keystone), flavor/image selection, network, security groups, SSH keypairs, floating IPs, and server metadata

Configuration flags

Flag	Env var	Description
--openstack-auth-url	WOODPECKER_OPENSTACK_AUTH_URL	Keystone endpoint
--openstack-username	WOODPECKER_OPENSTACK_USERNAME	Username
--openstack-password	WOODPECKER_OPENSTACK_PASSWORD	Password
--openstack-tenant-name	WOODPECKER_OPENSTACK_TENANT_NAME	Project/tenant name
--openstack-domain-name	WOODPECKER_OPENSTACK_DOMAIN_NAME	Domain (default: Default)
--openstack-region	WOODPECKER_OPENSTACK_REGION	Region
--openstack-flavor	WOODPECKER_OPENSTACK_FLAVOR	Flavor name or ID
--openstack-image	WOODPECKER_OPENSTACK_IMAGE	Image name or ID
--openstack-network	WOODPECKER_OPENSTACK_NETWORK	Network UUID
--openstack-security-groups	WOODPECKER_OPENSTACK_SECURITY_GROUPS	Security groups
--openstack-keypair	WOODPECKER_OPENSTACK_KEYPAIR	SSH keypair name
--openstack-floating-ip-pool	WOODPECKER_OPENSTACK_FLOATING_IP_POOL	Floating IP pool
--openstack-metadata	WOODPECKER_OPENSTACK_METADATA	Server metadata (key=value)

Test plan

• go build ./... compiles successfully
• go test ./... passes all tests
• Manual testing with an OpenStack environment (DevStack or real cloud)

Closes #278

[gerbsen]

I do also have interest in this feature and I do have an openstack cluster for testing available. Is this something you would consider merging?

[xoxys]

@gerbsen Help would be appreciated, however this PR looks like fully AI generated and incomplete. Especially the implemented tests are completely useless. Would you be able to finish/polish this PR?

[gerbsen]

Yeah, I've seen that this is generated by AI. :/ We will have to decide within our team, if we want to spent resources on this (there are some good arguments for it) but no final decision has been made. I just wanted to know first, if this would be something you would actually merge. I interpret your answer as a „yes”.

[gerbsen]

@xoxys not sure if you get notified on my comments in #278 but we made great progress and want to get this upstream if possible in the coming days: https://gitlab.com/alasca.cloud/focis/woodpecker-autoscaler/-/merge_requests/2