Update Spring to 5.1.8.RELEASE and spring-security-oauth2 to 2.3.6.RELEASE

[angelusGJ]

No description provided.

[codecov-io]

Codecov Report

Merging #1496 into master will increase coverage by <.01%.
The diff coverage is 28.57%.

@@             Coverage Diff              @@
##             master    #1496      +/-   ##
============================================
+ Coverage     25.21%   25.21%   +<.01%     
+ Complexity      912      907       -5     
============================================
  Files           209      209              
  Lines         11689    11647      -42     
  Branches       2116     2117       +1     
============================================
- Hits           2947     2937      -10     
+ Misses         8227     8195      -32     
  Partials        515      515

Impacted Files	Coverage Δ	Complexity Δ
...impl/DefaultJWTEncryptionAndDecryptionService.java	73.72% <ø> (ø)	29 <0> (ø)	⬇️
...2/service/impl/BlacklistAwareRedirectResolver.java	100% <ø> (ø)	3 <0> (-5)	⬇️
...client/service/impl/StaticSingleIssuerService.java	0% <0%> (ø)	0 <0> (ø)	⬇️
...id/connect/config/ConfigurationPropertiesBean.java	50.84% <0%> (-1.79%)	16 <0> (ø)
...n/java/org/mitre/openid/connect/web/ClientAPI.java	0% <0%> (ø)	0 <0> (ø)	⬇️
...rvice/impl/UriEncodedClientUserDetailsService.java	0% <0%> (ø)	0 <0> (ø)	⬇️
...ect/web/ProtectedResourceRegistrationEndpoint.java	0% <0%> (ø)	0 <0> (ø)	⬇️
...connect/web/DynamicClientRegistrationEndpoint.java	0% <0%> (ø)	0 <0> (ø)	⬇️
...service/impl/StaticServerConfigurationService.java	50% <100%> (ø)	3 <1> (ø)	⬇️
...t/client/service/impl/ThirdPartyIssuerService.java	78.57% <100%> (ø)	9 <1> (ø)	⬇️
... and 23 more

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[jricher]

Why was this change made? We moved to using PostConstruct many years ago, so I'm not sure why we'd move back.