Disable management.trace.http by default

[philwebb]

Currently we only offer InMemoryHttpTraceRepository and if actuator is present then we trace every request. This seems a little wasteful so perhaps we should disable support by default.

[philwebb]

See #14966

[philwebb]

Devtools could switch it back on perhaps.

[wilkinsona]

I'm not sure about changing the default in a maintenance release. Should this not wait for 2.2?

[philwebb]

Whoops, wrong milestone

[philwebb]

See also #8679