springboot Add support for nested requests in MetricsClientHttpRequestInterceptor

See gh-19381

Comment From: grahammkelly

Looks good and it addresses the issue.

Comment From: grahammkelly

Will/can this be backported to the 2.2 branch?

Comment From: wilkinsona

We can certainly consider it. IIRC, we only made the change in 2.3.x as we were concerned about the risk of a regression.