Fix to work with prometheus working in non-root

[Muxa1L]

Description

This fix is for prometheus connector, aimed to allow trino work with prometheus'es working in non-root url (or to work with victoriametrics in cluster mode, needing to use urls like /select//prometheus/api/.... )

Is this change a fix, improvement, new feature, refactoring, or other?
Fix
Is this a change to the core query engine, a connector, client library, or the SPI interfaces? (be specific)
Prometheus Connector
How would you describe this change to a non-technical end user or system administrator?
aimed to allow trino work with prometheus'es working in non-root url (or to work with victoriametrics in cluster mode, needing to use urls like /select//prometheus/api/.... )

Related issues, pull requests, and links

Documentation

( ) No documentation is needed.
( ) Sufficient documentation is included in this PR.
( ) Documentation PR is available with #prnumber.
( ) Documentation issue #issuenumber is filed, and can be handled later.

Release notes

( ) No release notes entries required.
( ) Release notes entries required with the following suggested text:

# Section
* Fix some things. ({issue}`issuenumber`)