[eslint-config-terra] Update dependencies

[sdadn]

Summary

This PR moves the eslint to peerDependencies. It was accidentally moved to dependencies as part of #811 . This unintended change resulted in webpack failures with NPM 6 as the dependencies weren't getting installed correctly. NPM 9 was not affected due to how it handles dependencies differently.

Testing

This change was tested using:

• [ ] WDIO
• [ ] Jest
• [ ] Visual testing (please attach a screenshot or recording)
• [x] Other (please describe below)
• [ ] No tests are needed

This change was tested by setting the dev environment to NPM 6 and running npm run clean:install && npm start on terra-framework locally. This resulted in the following failure:

This was again tested by running npm pack and using the local eslint-config-terra with npm install -D path/to/tgz which resulted in the same error.

The error was fixed by moving eslint to peerDepndencies and then repeating the steps above to test the change locally. The result was npm start successfully executing:

Reviews

In addition to engineering reviews, this PR needs:

• [ ] UX review
• [ ] Accessibility review
• [ ] Functional review
• [x] Tech verification

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Thank you for contributing to Terra. @cerner/terra

[kenk2]

Verified these changes locally:

• Ran npm run clean:install followed by npm start at the root level, the project ran successfully locally.
• Ran npm run pack at the project level, then installed the tarball as a dependency in terra-framework, the project ran successfully locally.