ref(tests): Move top-level jest config to jest folder

[lobsterkatie]

This moves our base jest config into a jest folder, in anticipation of more jest config files in future PRs. It also sets up those files to be linted, by adding the folder to our dev tsconfig and to our main eslint config.

[github-actions]

size-limit report 📦

Path	Size
@sentry/browser - ES5 CDN Bundle (gzipped + minified)	18.35 KB (-8.87% 🔽)
@sentry/browser - ES5 CDN Bundle (minified)	57.52 KB (-10.98% 🔽)
@sentry/browser - ES6 CDN Bundle (gzipped + minified)	17.13 KB (-9.17% 🔽)
@sentry/browser - ES6 CDN Bundle (minified)	51.75 KB (-10.73% 🔽)
@sentry/browser - Webpack (gzipped + minified)	20.94 KB (-9.88% 🔽)
@sentry/browser - Webpack (minified)	72.5 KB (-11.28% 🔽)
@sentry/react - Webpack (gzipped + minified)	20.98 KB (-9.89% 🔽)
@sentry/nextjs Client - Webpack (gzipped + minified)	45.97 KB (-4.34% 🔽)
@sentry/browser + @sentry/tracing - ES5 CDN Bundle (gzipped + minified)	24.14 KB (-7.44% 🔽)
@sentry/browser + @sentry/tracing - ES6 CDN Bundle (gzipped + minified)	22.65 KB (-7.51% 🔽)