Revive fledgling eslint config

[phillxnet]

We currently have an unused eslint configuration. On the Python linting side, core developers use default black. It is proposed that we re-visit our prior configuration of https://eslint.org/ to assist in our next testing phase: to be focused on front-end code tidy/update, complementing our near complete current testing phase of back-end/Python tidy/update.

Having our JS code linted to a common config is the aim here. Easing the likely many changes to come in the front-end JS code.

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Related/Foundational PR: #1635