fix(api): make the http header and request timeouts tunable (#2259)

deploy/self-hosting/.env.example

@@ -121,3 +121,12 @@ FLUXER_DISCOVERY_ENABLED=true
 # every service. The bundled compose talks to Postgres directly, where naming is
 # a win and the default is correct.
 #FLUXER_POSTGRES_PREPARED_STATEMENTS=true
+
+# The api bounds how long a client may take to send a request. The header timeout
+# covers the request line and headers only, while the request timeout covers the
+# whole exchange, so a slow uploader is bounded by the second value and not by
+# the first. Raise both if you front large uploads or serve clients on high
+# latency links. The header timeout is clamped down to the request timeout, so
+# raising it alone does nothing. Both are milliseconds, between 1000 and 3600000.
+#FLUXER_API_HEADERS_TIMEOUT_MS=30000
+#FLUXER_API_REQUEST_TIMEOUT_MS=120000