When @ConditionalOnBean or @ConditionalOnMissingBean are used on a
@Bean method, they will, in the absence of any other configuration,
attempt to deduce the bean's type by examining the method's return
type. This deduction can fail. See gh-4841, gh-4934, and gh-5624
for some examples of possible failure causes. Previously, this
failure was only logged as a debug message leaving the user with a
misleading message suggesting that the @ConditionalOnBean or
@ConditionalOnMissingBean annotation was not configured correctly.

This commit improves the diagnostics by mention the possibility of
type deduction in the exception message and including the exception
that caused deduction to fail as the cause.

Closes gh-4934