Cache evection of HTTP Client lead to not closed HttpClients

Describe the Bug

The current implementation of caching and evicting an HTTP Client lead to not closed HttpClients.

https://github.com/SAP/cloud-sdk-java/blob/4fb1f6a0a4a2517a10dc4b02c69a6f072d98db8a/cloudplatform/connectivity-apache-httpclient5/src/main/java/com/sap/cloud/sdk/cloudplatform/connectivity/DefaultApacheHttpClient5Cache.java#L42-L47

Technically the HttpClients are CloseableHttpClient and should / need(specifically for pooled connections) to be closed after usage.
(See also this discussion)

In the current code-base, when a HttpClient with a PoolingHttpClientConnectionManager is created, it's not cleaned up properly on eviction.

---

The following workaround does not work in all cases:

        cache = Caffeine.newBuilder().expireAfterAccess(duration, unit).ticker(ticker).evictionListener((key, value, cause) -> {
            if (value instanceof CloseableHttpClient closeableHttpClient) {
                try {
                    closeableHttpClient.close();
                } catch (final Exception e) {
                    log.warn("Failed to close HttpClient. Ignoring the exception and continue.", e);
                }
            }
        }).build();

There are two basic scenarios:

1. The client was created and is no longer in use and the eviction time triggers the cleanup. ✅
2. The client was created and in still in use (long running operation, async operation, ...) and the eviction time triggers the cleanup. Then the evictionListener would kill the connection underneath. ❌

Steps to Reproduce

Code review.

Expected Behavior

Proper closing of HttpClients.

Screenshots

No response

Used Versions

Current state in main.

Code Examples

// Your code here

Stack Trace

No response

Log File

Log file

...

Affected Development Phase

Development

Impact

No Impact

Timeline

No response

Comienza con DefaultApacheHttpClient5Cache.java en la construcción de la caché enlazada y revisa la discusión en el issue 755. Traza cómo se crean, almacenan en caché, expulsan y utilizan los CloseableHttpClients agrupados durante operaciones de larga duración o asíncronas; el trabajo está terminado cuando los clientes expulsados se cierran sin interrumpir a los clientes que aún están en uso.