docs: update for v0.5.0-affogato release

[vlatte]

• docs: update for v0.5.0-affogato release
  • go.mod
  • README.md
  • CHANGELOG.md
  • design documents

Tested with

• CB-Spider (https://github.com/cloud-barista/cb-spider/releases/tag/v0.4.19)
• CB-Tumblebug (https://github.com/cloud-barista/cb-tumblebug/releases/tag/v0.4.18)
• CB-Dragonfly (https://github.com/cloud-barista/cb-dragonfly/releases/tag/v0.4.4)