v0.5.0 compatible with ZIO 1.0.0-RC20

This release adds an opencensus client and compatibility with ZIO 1.0.0-RC20.

• Update zio, zio-test, zio-test-sbt to 1.0.0-RC19-2 (#156) by @scala-steward
• Add opencensus client (#155) by @frekw
• Upgrade ZIO to 1.0.0-RC20 (#160) by @ghostdogpr