Improve tracing

docs/content/observability/tracing/haystack.md

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+# Haystack
+
+To enable the Haystack:
+
+```toml tab="File"
+[tracing]
+  [tracing.haystack]
+```
+
+```bash tab="CLI"
+--tracing
+--tracing.haystack
+```
+
+#### `localAgentHost`
+
+_Require, Default="127.0.0.1"_
+
+Local Agent Host instructs reporter to send spans to haystack-agent at this address.
+
+```toml tab="File"
+[tracing]
+  [tracing.haystack]
+    localAgentHost = "127.0.0.1"
+```
+
+```bash tab="CLI"
+--tracing
+--tracing.haystack.localAgentHost="127.0.0.1"
+```
+
+#### `localAgentPort`
+
+_Require, Default=42699_
+
+Local Agent port instructs reporter to send spans to the haystack-agent at this port.
+
+```toml tab="File"
+[tracing]
+  [tracing.haystack]
+    localAgentPort = 42699
+```
+
+```bash tab="CLI"
+--tracing
+--tracing.haystack.localAgentPort=42699
+```
+
+#### `globalTag`
+
+_Optional, Default=empty_
+
+Apply shared tag in a form of Key:Value to all the traces.
+
+```toml tab="File"
+[tracing]
+  [tracing.haystack]
+    globalTag = "sample:test"
+```
+
+```bash tab="CLI"
+--tracing
+--tracing.haystack.globalTag="sample:test"
+```
+
+#### `traceIDHeaderName`
+
+_Optional, Default=empty_
+
+Specifies the header name that will be used to store the trace ID.
+
+```toml tab="File"
+[tracing]
+  [tracing.haystack]
+    traceIDHeaderName = "sample"
+```
+
+```bash tab="CLI"
+--tracing
+--tracing.haystack.traceIDHeaderName="sample"
+```
+
+#### `parentIDHeaderName`
+
+_Optional, Default=empty_
+
+Specifies the header name that will be used to store the span ID.
+
+```toml tab="File"
+[tracing]
+  [tracing.haystack]
+    parentIDHeaderName = "sample"
+```
+
+```bash tab="CLI"
+--tracing
+--tracing.haystack.parentIDHeaderName="sample"
+```
+
+#### `spanIDHeaderName`
+
+_Optional, Default=empty_
+
+Apply shared tag in a form of Key:Value to all the traces.
+
+```toml tab="File"
+[tracing]
+  [tracing.haystack]
+    spanIDHeaderName = "sample:test"
+```
+
+```bash tab="CLI"
+--tracing
+--tracing.haystack.spanIDHeaderName="sample:test"
+```
+
+#### `baggagePrefixHeaderName`
+
+_Optional, Default=empty_
+
+Specifies the header name prefix that will be used to store baggage items in a map.
+
+```toml tab="File"
+[tracing]
+  [tracing.haystack]
+    baggagePrefixHeaderName = "sample"
+```
+
+```bash tab="CLI"
+--tracing
+--tracing.haystack.baggagePrefixHeaderName="sample"
+```