feat: allow configuration to be overridden

[mattcan]

This PR enables the (long awaited) ability to override the telus-standard linting configuration. For some users, this will be a BREAKING change.

How do I know if this will be a breaking change for my project?

• You have already migrated to telus-standard and your project has a .eslintrc.* file
• You are migrating to telus-standard and keeping your *.eslintrc.* file

If you meet one of these criteria then when you upgrade to the latest version of telus-standard, your existing configuration will come into play and you may fail linting.

Please, how do I bring back semicolons?

If you don't have an .eslintrc.* file, create a new .eslintrc.js and add this:

module.exports = {
  rules: {
    semi: ['error', 'always']
  }
}

[mattcan]

Probably should merge as a breaking change? If anyone left their .eslintrc in the directory after adopting this project, it will suddenly come back to life.

I'll add some documentation.

[mattcan]

• Added a CHANGELOG.md that points to this PR
• Updated the PR description to better inform what this change is and help developers determine how they will be affected
• Changed migration steps in README.md

[github-actions]

🎉 This PR is included in version 2.0.0 🎉

The release is available on:

• GitHub release
• npm package (@latest dist-tag)

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