Switching to @Async

[mrm9084]

Description

Updates from CompletableFuture to @async. CompletableFuture causes issues in Java 11 with more than 2 CPUs.

[codecov-commenter]

Codecov Report

Merging #705 into 1.1.x will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##              1.1.x     #705   +/-   ##
=========================================
  Coverage     56.18%   56.18%           
  Complexity      754      754           
=========================================
  Files           181      181           
  Lines          3186     3186           
  Branches        233      233           
=========================================
  Hits           1790     1790           
  Misses         1261     1261           
  Partials        135      135           

Impacted Files	Coverage Δ	Complexity Δ
...loud/config/AppConfigurationAutoConfiguration.java	0.00% <ø> (ø)	0.00 <0.00> (ø)
...e/spring/cloud/config/AppConfigurationRefresh.java	88.88% <100.00%> (ø)	17.00 <1.00> (ø)

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