[download] Iss and jku matching should be done as URL matching

[aaperis]

Describe the bug Currently the matching is done via string matching:

if value.ISS == issuerValue && value.JKU == jkuValue

which causes problems if for example a trailing / is neglected somewhere.

Steps to reproduce

Remove or add a / in a iss or jku URL in the iss.json file of a local download instance and try again to access a dataset.

Expected behavior

• [ ] Matching is done on the URL level
• [ ] Tests verifying the fix are added

Estimation of size: small

Estimation of priority: medium