feat: add fluxer upstream source and self-hosting documentation

- Clone of github.com/fluxerapp/fluxer (official upstream)
- SELF_HOSTING.md: full VM rebuild procedure, architecture overview,
  service reference, step-by-step setup, troubleshooting, seattle reference
- dev/.env.example: all env vars with secrets redacted and generation instructions
- dev/livekit.yaml: LiveKit config template with placeholder keys
- fluxer-seattle/: existing seattle deployment setup scripts

fluxer/fluxer_devops/signoz/conf/clickhouse/custom-function.xml

@@ -0,0 +1,21 @@
+<functions>
+    <function>
+        <type>executable</type>
+        <name>histogramQuantile</name>
+        <return_type>Float64</return_type>
+        <argument>
+            <type>Array(Float64)</type>
+            <name>buckets</name>
+        </argument>
+        <argument>
+            <type>Array(Float64)</type>
+            <name>counts</name>
+        </argument>
+        <argument>
+            <type>Float64</type>
+            <name>quantile</name>
+        </argument>
+        <format>CSV</format>
+        <command>./histogramQuantile</command>
+    </function>
+</functions>