OTEL: hostname handling (#155)

Adjusted/Added keep-hostname() for opentelemetry

Author: zsoltgyulai94

doc/_admin-guide/060_Sources/102_OpenTelemetry/000_opentelemetry_source_options.md

@@ -71,6 +71,10 @@ destination {
 
 *Description:* This option configures the upper limit of in-flight gRPC requests per worker. It is advisd to set this value in the range of 10s or 100s when there are a high number of clients sending simultaneously. In an optimzed solution, the number of `workers()` and `concurrent-requests()` is greater than or equal to the number of clients. However, this can cause an increase in memory usage.
 
+## keep-hostname()
+
+The `syslog-ng-otlp()` and `opentelemetry()` sources ignore this option and use the hostname from the message as the `${HOST}`.
+
 ## log-fetch-limit()
 
 |   Type:|       number|

doc/_admin-guide/060_Sources/175_syslog-otlp/000_otlp_source_options.md

@@ -129,7 +129,9 @@ source {
 
 {% include doc/admin-guide/options/host-override.md %}
 
-{% include doc/admin-guide/options/keep-hostname.md %}
+## keep-hostname()
+
+The `syslog-ng-otlp()` and `opentelemetry()` sources ignore this option and use the hostname from the message as the `${HOST}`.
 
 {% include doc/admin-guide/options/keep-timestamp.md %}