More concise error message in the api-server log when `execution_api_server_url` isn't correct

### Description

When the `execution_api_server_url` config variable isn't correct, the consequences are:

- Tasks don't run successfully
- task state mismatch under Events tab in the UI https://github.com/apache/airflow/issues/50191

These don't explicitly identify the root cause.

### Use case/motivation

It should be easier to identify when something core in the configuration is misconfigured such that the different components of Airflow can't communicate with each other. This could be evident from:

* a configuration checker (like `airflow config check`)
* On the homepage of the UI? More details when one of the components has a big red X
* In the `api-server` log (or the scheduler log?)

### Related issues

The symptoms of misconfiguration were first identified here https://github.com/apache/airflow/issues/50191

### Are you willing to submit a PR?

- [ ] Yes I am willing to submit a PR!

### Code of Conduct

- [x] I agree to follow this project's [Code of Conduct](https://github.com/apache/airflow/blob/main/CODE_OF_CONDUCT.md)

Start by tracing how the `execution_api_server_url` configuration is handled and how the api-server currently logs failures. Review related issue #50191 and compare the proposed configuration checker, UI, and api-server or scheduler log surfaces; done means the misconfiguration's root cause is identified clearly in one chosen surface.

Written by the indexing model from the issue text.