Update SpringBootTestContextBootstrapper to detect `@ContextHierarchy`
annotations so that only the last child creates a
`WebApplicationContext`.

Prior to this commit a context hierarchy would start two embedded web
servers which is inconsistent with the `SpringApplicationBuilder`
behavior.

Fixes gh-8311

Allow `PathExtensionContentNegotiationStrategy` to be bypassed by
actuator endpoints. Prior to this commit calling `/loggers/com.aaa.cab`
would return a HTTP 406 response due to `.cab` being a known extension.

Fixes gh-8765

* pull8924:
  Fail fast on getKeyFromServer() failure

Update `ResourceServerTokenServicesConfiguration` to fail fast if the
`getKeyFromServer()` call fails. Since the key is part of the singleton
`JwtAccessTokenConverter` bean there is not real way to refresh without
restarting the application.

A hard failure seems preferable to an inconsistent state.

Closes gh-8924

Closes gh-8497

* pr/8906:
  Polish "Fix statsd metrics collection for names with ":""
  Fix statsd metrics collection for names with ":"

Closes gh-8906

Statsd server is ignoring malformed metrics. This change introduces
a basic sanitizing to metric names for avoid losing those metrics.

See gh-8906

Rename `AbstractTemplateAvailabilityProvider` to
`PathBasedTemplateAvailabilityProvider`.

Closes gh-8913

Closes gh-8672

Closes gh-8903

Closes gh-8592

* pr/8889:
  Upgrade to Apache Maven 3.5.0

Closes gh-8889

Closes gh-8895

Closes gh-8892

Closes gh-8232

Closes gh-6911

This commit makes sure to honour the `spring.aop.proxy-target-class`
property if set by the user. Previously, the
`PersistenceExceptionTranslationPostProcessor` was always configured to
use cglib, regardless of the value of that property.

Closes gh-8887

Closes gh-8497

Fixes gh-8883

This commit makes sure to honour the `spring.aop.proxy-target-class`
property if set by the user. Previously, the
`MethodValidationPostProcessor` was always configured to use cglib,
regardless of the value of that property.

Closes gh-8869