feat(new-rule-option): improve strict-boolean-expressions by adding allow-enum

[atsu85]

PR checklist

• Addresses an existing issue: strict-boolean-expressions: add config option to disable warnings in case of enums #3571
• New feature(rule option), enhancement for "strict-boolean-expressions" rule
  • Includes tests
• Documentation update

Overview of change:

Added new configuration option "allow-enum", that disables errors when using enum in boolean expression, so that error wouldn't be emitted

Is there anything you'd like reviewers to focus on?

I've added the motivation and detailed description to the issue #3571 - take a look at that as well.

I had 2 ideas to avoid emitting enum related errors:

This PR addresses that issue using approach b described in that issue.

CHANGELOG.md entry:

[new-rule-option] strict-boolean-expressions adds allow-enum to allow using enums in boolean expressions

[palantirtech]

Thanks for your interest in palantir/tslint, @atsu85! Before we can accept your pull request, you need to sign our contributor license agreement - just visit https://cla.palantir.com/ and follow the instructions. Once you sign, I'll automatically update this pull request.

[atsu85]

@ajafff, @adidahiya could You review this PR?