Lease API, Multiple CA certs & Credentials plugin support

New features:

• Adds support for k8s lease resources [#120 by @BrainHorse]
• Support multiple ca certs for trust manager [#136 by @petern-sc]
• Credentials plugin support [#133 by @yurique]

Other:

• Tests against Kubernetes 1.21, 1.22 and 1.23 [#165 by @joan38]