[Feature]: Oracle Cloud Infrastructure backend

[jvstme]

Add support for Oracle Cloud Infrastructure. The main priority is on-demand GPU instances. Support for other types of instances may be added later.

Tasks

Essential, cannot release the feature without these:

• backend configuration
• instances catalog in gpuhunt
• getting offers in dstack
• packer templates
• running images from the marketplace
• running and terminating instances
• controlling disk size
• creating network resources
• creating compartments
• client credentials without file paths
• docs

Non-essential, may be added after the release:

• document restrictive permissions
• GitHub actions for publishing packer images
• creating dstack gateways
• multi-node tasks
• bare metal instances
• local disks
• always free instances
• preemptible (spot) instances
• flexible instances