Make transactions endpoint pagination consistent - Closes #1884

[Tschakki]

What was the problem?

In case the first sorting param for transaction is not precise enough, pagination of the transactions endpoint was not consistent.

How did I fix it?

Added a second sorting param, which determines the order in that the transactions get returned, if the first sorting param is not precise enough.

How to test it?

the last entry of this call:
http://localhost:4000/api/transactions?blockId=6524861224470851795&sort=timestamp:desc&offset=0&limit=51
and the first entry of this call:
http://localhost:4000/api/transactions?blockId=6524861224470851795&sort=timestamp:desc&offset=50&limit=51
should be always identical.

Review checklist

• The PR solves Inconsistent response for /transactions endpoint  #1884
• All new code is covered with unit tests
• All new code was formatted with Prettier
• Linting passes
• Tests pass
• Commit messages follow the commit guidelines
• Documentation has been added/updated