Web console: Remove support for IE11 and other older browsers

[jgoz]

Description

There are some ES6 features, such as Proxy, that would make sense to use in various parts of the web console. Unfortunately, many of these cannot be polyfilled and therefore cannot be used in older browsers like IE11.

Since IE11 will be officially retired in about 1 year and its rendering engine still exists inside of the new Edge for those who need it, there is no compelling reason to continue supporting it in the web console. Dropping IE and other browsers that lack ES6 support will both slim down the JS payload and allow us to use new ES features that have ostensibly been available for a few years in the majority of browsers.

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Key changes

• Consolidate and update browserslist declaration to include only those browsers that support ES6
• Update TypeScript compilation target to es2016
• Add a banner to unified-console.html if an unsupported browser is detected (using existence of Proxy as a rough indicator of support)
• Replace HotkeysTarget usage (deprecated) with useHotkeys to avoid runtime error caused by dependence on ES5-style class behavior

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This PR has:

• been self-reviewed.
• been tested in a test Druid cluster.
• added or updated version, license, or notice information in licenses.yaml

[vogievetsky]

I had one wording suggestion but otherwise this looks great. Very excited about all the cool stuff we can do with the newer JS target

[suneet-s]

Added Release Notes label to warn users who might be using some of these older browsers. Hopefully no one :)