Rule to enforce parameter type declaration of `unknown` for catchError()

[felixfbecker]

The time has finally come that TypeScript v4 added the ability to explicitly declare catch bindings as unknown instead of any and the next version of typescript-eslint will come with a rule to enforce the usage of unknown for all catch clauses, finally making them type safe.

The only puzzle piece missing then is the same for catchError() bindings in Rx. These are any in the typings by default (the same as with TypeScript v4's catch clauses), but them being any, they can be manually declared to be unknown instead. It would be awesome to have a rule that enforces this, with an autofixer. It should also forbid any other types to be used (those can be explicitly casted if needed).

[cartant]

There is now a no-implicit-any-catch rule in this package - to handle catchError operators - and there's a no-implicit-any-catch rule in eslint-plugin-etc, too - to handle promise rejections in catch and then calls.