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

Bắt đầu với DefaultApacheHttpClient5Cache.java tại phần xây dựng cache được liên kết và xem lại thảo luận trong issue 755. Theo dõi cách các CloseableHttpClients dùng chung được tạo, lưu vào cache, loại bỏ và sử dụng trong các thao tác chạy lâu hoặc bất đồng bộ; hoàn thành khi các client đã bị loại bỏ được đóng mà không làm gián đoạn các client vẫn đang được sử dụng.