PBM-1728 Support workload federation for OCI

[jcechace]

ticket: https://perconadev.atlassian.net/browse/PBM-1728
related to: #1318

• Adds support for instance principal auth
• Adds support for OKE workload identity
• Credentials shape changed to accommodate the different types of authentication

Example configuration

storage:
  type: oci
  oci:
    region: eu-frankfurt-1
    namespace: idvufsl0apl6
    bucket: pbm-test-jakub
    prefix: pbm
    maxObjSizeGB: 1
    retryer:
      maxAttempts: 15
      maxBackoff: 180s
    credentials:
      type: userPrincipal # instancePrincipal | okeWorkloadIdentity
      userPrincipal:
        tenancy: ocid1.tenancy.oc1..xxx
        user: ocid1.user.oc1..yyy
        fingerprint: e0:a8:24:e5:f6:b8:6e:...
        privateKey: |
          -----BEGIN PRIVATE KEY-----

          ...
          -----END PRIVATE KEY-----

[boris-ilijic]

LGTM, there are 2 additional things:

• pbm-conf-reference.yml needs to be updated :)
• I'd include full oci config within PR description as example (it handy to copy-paste it from PR when you need it)