chore(relay): specify spool.enveloppe.max_backpressure_memory_percent configuration for handling relay's failing healthcheck (#3635)

* chore(relay): specify spool.enveloppe.max_backpressure_memory_percent configuration for handling relay's failing healthcheck

Although a fix is being rolled out, that does not mean every relay instance would suddenly be fixed. We would need to still provide a workaround for people to try out. Refer to this specific issue comment: #3330 (comment)

* Update config.example.yml

Co-authored-by: Riccardo Busetti <riccardob36@gmail.com>

* chore: default path for relay spool envelopes

---------

Co-authored-by: Riccardo Busetti <riccardob36@gmail.com>

Author: aldy505

relay/config.example.yml

@@ -14,13 +14,18 @@ processing:
 
 # In some cases, relay might fail to find out the actual machine memory
 # therefore it makes the healthcheck fail and events can't be submitted.
-# As a workaround, uncomment the following line:
+# See https://github.com/getsentry/self-hosted/issues/3330 for more details.
+# As a workaround, uncomment the following `health` and `spool` sections:
 #
 # health:
 #  max_memory_percent: 1.0
+# spool:
+#   envelopes:
+#     path: "/tmp/relay-spool-envelopes"
+#     max_backpressure_memory_percent: 1.0
 
 # If you have statsd server, you can utilize that to monitor self-hosted Relay.
-# To start, uncomment the following line and adjust the options as needed.
+# To start, uncomment the following `metrics` section and adjust the options as needed.
 #
 # metrics:
 #  statsd: "100.100.123.123:8125" # It is recommended to use IP address instead of domain name