refactor(stark-core): refactor logic to validate StarkSessionConfig to prevent Angular AOT error "Function calls are not supported in decorators"

[christophercr]

ISSUES CLOSED: #797

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/NationalBankBelgium/stark/blob/master/CONTRIBUTING.md#-commit-message-guidelines
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

[X] Bugfix
[ ] Feature
[ ] Code style update (formatting, local variables)
[X] Refactoring (no functional changes, no api changes)
[ ] Build related changes
[ ] CI related changes
[ ] Documentation content changes
[ ] Other... Please describe:

What is the current behavior?

Issue Number: #797 #727

What is the new behavior?

AOT Production build succeeds even if a session config object is passed to the SessionModule.forRoot().

Does this PR introduce a breaking change?

[ ] Yes
[X] No

[coveralls]

Coverage increased (+0.2%) to 91.424% when pulling ea8c18c on christophercr:feature/fix-aot-session-module into ccade91 on NationalBankBelgium:master.