Split LogRequests middleware into multiple middlewares

[Turbo87]

The LogRequests middleware is currently performing multiple tasks:

• Save req.path() before the NormalizePath middleware potentially mutates the request path
• Calculate response timing based on the x-request-start HTTP header from Heroku (or the StartInstant extension as a fallback)
• Log requests to stdout
• Report errors to Sentry

The Sentry error reporting was originally built into the LogRequests middleware because it also needed access to the original path and the response timing.

This PR proposes to split the LogRequests middleware, so that each middlewares is performing only one of the functions respectively:

• The "original path" code is moved into the NormalizePath middleware that is responsible for mutating the path in the first place
• The request timing code is moved into a new RequestTiming middleware, which saves the response time in the request extension map
• The Sentry error reporting code is moved into a new SentryMiddleware

[bors]

☔ The latest upstream changes (presumably #3904) made this pull request unmergeable. Please resolve the merge conflicts.

[bors]

☔ The latest upstream changes (presumably #3988) made this pull request unmergeable. Please resolve the merge conflicts.

[bors]

☔ The latest upstream changes (presumably #4036) made this pull request unmergeable. Please resolve the merge conflicts.

[Turbo87]

closing in favor of #4137