Add info on default_cache_expiration (#896)

Include `default_cache_expiration` in the following instructions:

* Read Example
* Cache Example

Relates-To: OLPEDGE-2004

Signed-off-by: Halyna Dumych <ext-halyna.dumych@here.com>

Author: HalynaDumych

docs/dataservice-cache-example.md

@@ -111,9 +111,21 @@ You need to create the `OlpClientSettings` object to get catalog and partition m
 
 3. [Authenticate](#authenticate-to-here-olp-using-client-credentials) to the HERE platform.
 
-4. Set up the `OlpClientSettings` object with the path to the needed cache settings properties (the limit of runtime memory, disk space, maximum file size, memory data cache size, options, and paths).
-  For instructions on how to get the path to the cache settings, see the [Build and Run on Linux](#build) section.
-  > **Note:** Perform the first call with the valid mutable cache path, and the second call – with the protected cache path.
+4. (Optional) For data that is stored in the cache, to add expiration limit, set the `default_cache_expiration` to the needed expiration time.
+
+   By default, expiration is disabled.
+
+   > Note: You can only disable expiration for the mutable and in-memory cache. This setting does not affect the protected cache as no entries are added to the protected cache in the read-only mode.
+
+   ```cpp
+   std::chrono::seconds default_cache_expiration = std::chrono::seconds(200);
+   ```
+
+5. Set up the `OlpClientSettings` object with the path to the needed cache settings properties (the limit of runtime memory, disk space, maximum file size, memory data cache size, options, and paths).
+
+   For instructions on how to get the path to the cache settings, see the [Build and Run on Linux](#build) section.
+
+   > **Note:** Perform the first call with the valid mutable cache path, and the second call – with the protected cache path.
 
    ```cpp
    client_settings.cache =

docs/dataservice-read-catalog-example.md

@@ -215,7 +215,17 @@ You need to create the `OlpClientSettings` object to get catalog and partition m
 
 3. [Authenticate](#authenticate-to-here-olp-using-client-credentials) to the HERE platform.
 
-4. Set up the `OlpClientSettings` object.
+4. (Optional) For data that is stored in the cache, to add expiration limit, set the `default_cache_expiration` to the needed expiration time.
+
+   By default, expiration is disabled.
+
+   > Note: You can only disable expiration for the mutable and in-memory cache. This setting does not affect the protected cache as no entries are added to the protected cache in the read-only mode.
+
+   ```cpp
+   std::chrono::seconds default_cache_expiration = std::chrono::seconds(200);
+   ```
+
+5. Set up the `OlpClientSettings` object.
 
    ```cpp
    olp::client::OlpClientSettings client_settings;
@@ -224,6 +234,7 @@ You need to create the `OlpClientSettings` object to get catalog and partition m
    client_settings.network_request_handler = std::move(http_client);
    client_settings.cache =
        olp::client::OlpClientSettingsFactory::CreateDefaultCache({});
+   client_settings.default_cache_expiration = std::chrono::seconds(200);
    ```
 
 The `OlpClientSettings` class pulls together all the settings for customization of the client library behavior: