fix: next_page_token when runs exhaust

[JaeAeich]

Describe the bug
The next_page_token should return empty when the number of runs have exhausted. while fetching runs, I set the pageSize to 10, number of runs available were 7, I still got next_page_token which led me to another fetch call which returned empty list of runs.

To Reproduce
Steps to reproduce the behavior:
keep fetching runs till they exhaust.

Additional context
I encountered it while working on WES component where the Web Component was paginating to an empty list of runs. I have tried local dev branch.

[uniqueg]

I suppose this is the same issue as this one: elixir-cloud-aai/proTES#165

For anyone implementing this, it might actually be good to externalize the pagination logic and put it as a utility in FOCA, i.e., here, then import it in both proTES and proWES.

At some point, we could also think about creating a dedicated foca-utils package for these commonly (re)used utils.

[uniqueg]

@alohamora: Do you wanna look into that, perhaps? We may need this in our Service Registry API implementation as well. However, you would need to check whether those specs imply the same or a different pagination logic. If the latter, we might need to write logic for both.