🐛 Bug Report: Workflow link only works on CircleCI Cloud offering

> Moved an open issue from the Backstage/backstage org repo over to here
> Reference history and comment trail here: https://github.com/backstage/backstage/issues/16193

### 📜 Description

A new feature to link a CircleCI workflow (the term for the highest level of pipeline object in the service) was released via https://github.com/backstage/backstage/pull/15782 which helps improve the interface and jump users directly to a workflow by clicking the workflow ID in the CI Table. This link currently hardcodes in the CircleCI Cloud SaaS Offering URL of `app.circleci.com`.

Any user who uses the hosted/on-prem version of CircleCI (e.g., `circleci.mycompany.com`), these workflow links won't work.

### 👍 Expected behavior

A user with an on-prem/hosted version of CircleCI should be able to click the workflow link and bring up the workflow on their dedicated service.

### 👎 Actual Behavior with Screenshots

A user who clicks a workflow link will be brought to an HTTP 404 page on CircleCI's cloud offering.

### 👟 Reproduction steps

Use the latest version of the CircleCI Plugin with an on-prem offering, and click the link for a workflow.

### 📃 Provide the context for the Bug.

https://github.com/backstage/backstage/pull/15782

### 🖥️ Your Environment

_No response_

### 👀 Have you spent some time to check if this bug has been raised before?

- [X] I checked and didn't find similar issue

### Are you willing to submit PR?

None

Start by reviewing the workflow-link feature in Backstage pull request 15782 and tracing the CircleCI plugin's workflow URL construction. Reproduce the link with an on-premise base URL such as circleci.mycompany.com; done means hosted links open on that service while cloud links continue to work.

Written by the indexing model from the issue text.