Update boilerplate headers to Kubernetes standard

[TineoC]

Description

Update copyright headers in code files to use the Kubernetes standard boilerplate per the donated repository rules:

Additions of the standard Kubernetes header to code created by the contributors can occur post-transfer, but should ideally occur shortly thereafter.

Current State

Some files have headers like:

• Copyright 2020 The Elekto Authors
• Copyright 2020 Manish Sahani

These should be updated to:

• Copyright The Kubernetes Authors

Affected Repositories

• elekto-dev/elekto
• elekto-dev/docs
• elekto-dev/elekto.meta.test
• elekto-dev/elekto.meta.template

Tasks

• Update headers in elekto/ Python files
• Update headers in elekto/ non-Python files (Dockerfile, etc.)
• Add headers to docs/ files where missing
• Add headers to elekto.meta.test/ files
• Add headers to elekto.meta.template/ files

Reference

• Parent issue: Elekto to become kubernetes subproject #121
• Standard Kubernetes header