Upgrade dependencies

[ogero]

This PR upgrades the beat dependencies:

• libbeat was upgraded to github.com/elastic/beats/v7 v7.15.1
  it's go module replacements were copied from https://github.com/elastic/beats/blob/v7.15.1/go.mod
• containerd version was fixed to github.com/containerd/containerd v1.4.11 to address a dependabot alert
• dependencies were re-vendored