Remove val usage in TokenProvider

[emilpaw]

A part towards #306

[sendilkumarn]

Thanks @emilpaw for the contribution 🎉

(Congrats on your first contribution)

This looks good! I started the CI will merge it when it finishes.

[sendilkumarn]

@emilpaw can you please take a look at the build? there are few failures..

[emilpaw]

@sendilkumarn Many of the failing tests have definitely nothing to do with my changes. e.g. all the React tests fail because of this issue: #330
The ngx-gradle-fr test also fails because of some frontend related issue: https://github.com/jhipster/jhipster-kotlin/runs/5526701353?check_suite_focus=true

I'd like to wait until the issues are resolved before I continue to work on this PR.

[sendilkumarn]

Closing this in favor of #335