fix: Construction of OIDC endpoint when rootPath has a trailing slash

[sbernauer]

Description

Part of stackabletech/operator-rs#910

Before this PR the operator generated
http-server.authentication.oauth2.issuer=https\://185.56.150.115\:30584/realms/demo/
resulting in
java.lang.IllegalStateException: Invalid response from OpenID Metadata endpoint. The value of the "issuer" claim in Metadata document different than the Issuer URL used for the Configuration Request.

Definition of Done Checklist

• Not all of these items are applicable to all PRs, the author should update this template to only leave the boxes in that are relevant
• Please make sure all these things are done and tick the boxes

# Author
- [ ] Changes are OpenShift compatible
- [ ] CRD changes approved
- [ ] CRD documentation for all fields, following the [style guide](https://docs.stackable.tech/home/nightly/contributor/docs/style-guide).
- [ ] Helm chart can be installed and deployed operator works
- [ ] Integration tests passed (for non trivial changes)
- [ ] Changes need to be "offline" compatible

# Reviewer
- [ ] Code contains useful comments
- [ ] Code contains useful logging statements
- [ ] (Integration-)Test cases added
- [ ] Documentation added or updated. Follows the [style guide](https://docs.stackable.tech/home/nightly/contributor/docs/style-guide).
- [ ] Changelog updated
- [ ] Cargo.toml only contains references to git tags (not specific commits or branches)

# Acceptance
- [ ] Feature Tracker has been updated
- [ ] Proper release label has been added
- [ ] [Roadmap](https://github.com/orgs/stackabletech/projects/25/views/1) has been updated

[sbernauer]

Started https://testing.stackable.tech/view/02%20Operator%20Tests%20(custom)/job/trino-operator-it-custom/25/

[lfrancke]

Did this make it into 24.11?

[sbernauer]

Nope, but it will be part of 24.11.1. Not sure what label we should use here ^^