Bump ESLint dependencies

[ryoarmanda]

What is the purpose of this pull request?

• Documentation update
• Bug fix
• Feature addition or enhancement
• Code maintenance
• Others, please explain: Dependency update

In preparation on adding eslint-config-airbnb-typescript (the Typescript variant of the Airbnb style guide) for #1421, bumped some dependencies regarding to ESLint and other related dependencies.

Overview of changes:
Bumped eslint, eslint-plugin-import, and eslint-config-airbnb-base to the latest version.

• For the case of eslint, it is bumped to the highest v7 version (though v8 is already available).
• For the case of eslint-config-airbnb-base, the version after the current one jumps to 15.0.0

Anything you'd like to highlight / discuss:

The eslint-config-airbnb-base bump reports new lint errors to our current codebase, particularly due to some rules that were not enabled before and are enabled now:

• prefer-regex-literals (~11 new errors)
• default-param-last (~2 new errors)
• function-call-argument-newline (most new errors are from this rule, ~29)

I turned all of them off now, but we can discuss below whether we can enable some of the rules and fix some of the violations in this PR, in a separate PR, or keep them disabled.

My opinions:

• prefer-regex-literals: Should enable, fix the violations.
• default-param-last: Might enable it, but fixing the violation is a little work (the offender is the Site constructor). Can leave it off too.
• function-call-argument-newline: Keep it turned off. There's too much cases of both newline and non-newline function calls in our code. Enabling it for one option makes the other case look worse stylistically.

Testing instructions:
Check npm run lint, should be okay.

Proposed commit message: (wrap lines at 72 characters)
Bump ESLint dependencies

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Checklist: ☑️

• Updated the documentation for feature additions and enhancements
• Added tests for bug fixes or features
• Linked all related issues
• No unrelated changes

[jonahtanjz]

LGTM 👍

I turned all of them off now, but we can discuss below whether we can enable some of the rules and fix some of the violations in this PR, in a separate PR, or keep them disabled.

I think we can fix the regex one as well and keep the rest off for now. Doing it in another PR is fine. Just need to open an issue for this so we don't forget about it :)