Lint .mjs (et al)

[dominykas]

Support plan

• is this issue currently blocking your project? (yes/no): yeah, kind of
• is this issue affecting a production system? (yes/no): nah

Context

• node version: v16.x
• module version: v25.x
• environment (e.g. node, browser, native): node
• used with (e.g. hapi application, another framework, standalone, ...): hapi app, kind of
• any other relevant information:

What problem are you trying to solve?

.mjs files should be linted, as well as .js (and .cjs, I guess)

Do you have a new or modified API suggestion to solve the problem?

Pass extensions into eslint options - happy to PR...

[dominykas]

Or should I just stick to lintOptions?