Refactor initial CSRF creation into an Effect

[tdonohue]

In #2886, code was added to the request.service.ts which initializes the CSRF token if one does not already exist.

In the below comment, @atarix & @artlowel agreed that this should be refactored into request.effect.ts to avoid a nested subscription:

@artlowel @tdonohue
Looking at the #2886 i'm wondering if the code added here should be refactored in a better way.
I think the better place to do that check is the effect related to the dispatched ngrx action (https://github.com/DSpace/dspace-angular/blob/main/src/app/core/data/request.effects.ts#L43). In this way we avoid to add a nested subscription.
@artlowel do you agree? if so i can do the change in this PR

Originally posted by @atarix83 in #2871 (comment)

@atarix83 I agree that refactor would be a good idea, However I wouldn't hold up this PR to do it. I'd rather do it in a small bugfix PR next week.

Originally posted by @artlowel in #2871 (comment)

[tdonohue]

@atarix83 : Assigning this to you as you volunteered to do this. This refactor can be done in combination with one of the other PRs (Angular 17 upgrade or similar) that are on your plate. Thanks!