Add beta support for Oracle Cloud

[TheOnlyOne001]

Closes #102.

Summary

• add an oracle provider backed by the official OCI Go SDK
• wire the provider into the autoscaler CLI and provider flag registration
• launch agents with cloud-init user data, SSH authorized key metadata, pool/image freeform tags, subnet/VNIC config, and optional flexible shape sizing
• list and terminate only instances tagged for the configured autoscaler pool
• document the required Oracle Cloud environment variables

Validation

• docker run --rm -v ${PWD}:/work -w /work golang:1.26.3 go test ./providers/oracle
• docker run --rm -v ${PWD}:/work -w /work golang:1.26.3 go test ./...

Notes

This was tested with mocked OCI compute client calls rather than live OCI credentials. The tests cover launch request construction, user-data encoding, pool/state filtering with pagination, termination lookup, duplicate-instance safety, and client error wrapping.

[6543]

@TheOnlyOne001 sorry for the late review ... it mostly looks clean ... could you:

• resolve the git conflicts
• move types and error definitins into types.go file
• move helper func into helper.go
• fix lint issue (https://ci.woodpecker-ci.org/repos/8975/pipeline/3095/9) -> make a named const out of it

[6543]

ah and mark support as beta in readme see #671

as we maintainers have no access to oracle cloud to test out