Add option tlsIntercept

[lipsumar]

This PR adds an option tlsIntercept to MockttpHttpsOptions. This option is the inverse of the existing tlsPassthrough:

• tlsPassthrough: intercept everything except hostnames in this list
• tlsIntercept: intercept nothing except hostnames in this list

Both options can not be used at the same time.

This option allows mockttp to be less intrusive and to let most requests untouched, except for a specific list of hostnames. This helps keep some applications using certificate pinning working correctly.

Related issue: #162

@pimterry let me know if you'd prefer more tests and/or if docs need to be adjusted.

[CLAassistant]

All committers have signed the CLA.

[lipsumar]

@pimterry sorry for the delay on signing the CLA, I needed approval. We're all set!

[pimterry]

Thanks for that @lipsumar. The changes all look good here. Unfortunately though the CI tests have highlighted that the current test suite fails in the latest version of Node that was just released (v20.12.0) due to some kind of HTTP/2 changes, so I'm going to need to get that resolved before merging.

I'll look into that shortly and let you know once it's sorted so we can rebase this & merge it happily.

[pimterry]

Thanks @lipsumar! Rebased & merged 👍. I've renamed the option slightly here and gone for tlsInterceptOnly to make it a bit clearer what this is doing.

I'll release this shortly as part of v3.11.0.

[lipsumar]

tlsInterceptOnly makes a lot of sense, good call 👍 Thanks for your reactivity !