i18n - rules & metrics: create ESlint rule

[eledobleefe]

First step of the 'i18n - rules & metrics' project.

Objective: Create an ESlint rule that only allows string literals when they are wrapped up by the <Trans> tag.

[grafanabot]

@eledobleefe please add one or more appropriate labels. Here are some tips:

• if you are making an issue, TODO, or reminder for yourself or your team, please add one label that best describes the product or feature area. Please also add the issue to your project board. 🚀

• if you are making an issue for any other reason (docs typo, you found a bug, etc), please add at least one label that best describes the product or feature that you are discussing (e.g. area/alerting, datasource/loki, type/docs, type/bug, etc). Our issue triage doc also provides additional guidance on labeling. 🚀

Thank you! ❤️