Add per grant type configuration options

[HypeMC]

Resolves #105.

[codecov-io]

Codecov Report

Merging #199 into v3.x will increase coverage by 0.83%.
The diff coverage is 99.19%.

@@             Coverage Diff              @@
##               v3.x     #199      +/-   ##
============================================
+ Coverage     91.95%   92.79%   +0.83%     
- Complexity      386      395       +9     
============================================
  Files            58       58              
  Lines          1342     1415      +73     
============================================
+ Hits           1234     1313      +79     
+ Misses          108      102       -6     

Impacted Files	Coverage Δ	Complexity Δ
OAuth2Grants.php	0.00% <0.00%> (ø)	1.00 <0.00> (ø)
DependencyInjection/Configuration.php	100.00% <100.00%> (ø)	14.00 <3.00> (+9.00)
DependencyInjection/TrikoderOAuth2Extension.php	92.00% <100.00%> (+0.13%)	27.00 <0.00> (ø)

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[GordonGuenther]

Would this PR also allow to enable and configure custom grant types?

[X-Coder264]

@GordonGuenther You can already enable and configure custom grant types without this PR -> https://github.com/trikoder/oauth2-bundle/blob/v3.x/docs/implementing-custom-grant-type.md