feat: added missing features

[rglauco]

added federation_entity metadata parameters, policy page, federation resolve endpoint in example app

[codecov]

Codecov Report

Attention: 51 lines in your changes are missing coverage. Please review.

Comparison is base (82a8dd4) 91.23% compared to head (f824f2b) 91.26%.

Additional details and impacted files

@@             Coverage Diff              @@
##               main      #28      +/-   ##
============================================
+ Coverage     91.23%   91.26%   +0.02%     
- Complexity      774      789      +15     
============================================
  Files            47       47              
  Lines          2339     2380      +41     
  Branches        300      298       -2     
============================================
+ Hits           2134     2172      +38     
+ Misses          108      107       -1     
- Partials         97      101       +4     

Files	Coverage Δ
...in/java/it/spid/cie/oidc/config/OIDCConstants.java	0.00% <ø> (ø)
.../it/spid/cie/oidc/handler/RelyingPartyHandler.java	85.84% <100.00%> (+0.25%)	⬆️
...va/it/spid/cie/oidc/model/EntityConfiguration.java	89.57% <100.00%> (+0.16%)	⬆️
.../java/it/spid/cie/oidc/model/FederationEntity.java	100.00% <100.00%> (ø)
...a/it/spid/cie/oidc/config/RelyingPartyOptions.java	94.33% <80.76%> (-0.69%)	⬇️
...java/it/spid/cie/oidc/model/TrustChainBuilder.java	83.62% <83.62%> (+0.29%)	⬆️

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