Warn about too broad tracing configs

Tracing requests can make them more expensive (e.g. if there are
expensive logs that are only written when a request is traced). Enabling
tracing for too many requests can severely impact the performance and
the availability of the server, hence add a warning about this.

Bug: Google b/355393970
Release-Notes: skip
Change-Id: I140ae01421e34fd24e887e63952a86e1096bacc5
Signed-off-by: Edwin Kempin <ekempin@google.com>

Documentation/config-gerrit.txt

diff --git a/Documentation/config-gerrit.txt b/Documentation/config-gerrit.txt
index f274a3e..e862e3f 100644
--- a/Documentation/config-gerrit.txt
+++ b/Documentation/config-gerrit.txt
@@ -5896,6 +5896,11 @@
 `projectPattern`, or otherwise it is ignored. The subsection name is used as
 trace ID. Using this trace ID administrators can find matching log entries.
 
+[WARNING] Tracing requests can make them more expensive. To avoid performance
+issues trace configs should match as little requests as possible and only be
+added temporarily. Enabling tracing for too many requests can severely impact
+the performance and the availability of the server.
+
 [[tracing.traceid.requestType]]tracing.<trace-id>.requestType::
 +
 Type of request for which request tracing should be always enabled (can