Standardize TraceId/SpandId/TraceFlags field casing in log formats (o…

…pen-telemetry#1283)

OTLP/JSON is currently using trace_id, span_id field naming. The snake case
with underscores comes from Protobuf/JSON mapping rules.

Elsewhere we were previously using traceid, spanid, traceflags without underscores.

This changes standardizes field names to use underscores for all text log mediums
where these fields may be recorded.

Note: the alternate approach, i.e. keeping traceid, spanid, traceflags and renaming
them in OTLP/JSON would result in OTLP/JSON format having an inconsistent naming,
since all other fields use snake casing.

specification/logs/overview.md

@@ -417,9 +417,9 @@ so that they include the Request Context information in the emitted logs.
 trace context should be recorded in logs. To summarize, the following field
 names should be used in legacy formats:
 
-- "traceid" for [TraceId](data-model.md#field-traceid), hex-encoded.
-- "spanid" for [SpanId](data-model.md#field-spanid), hex-encoded.
-- "traceflags" for [trace flags](data-model.md#field-traceflags), formatted
+- "trace_id" for [TraceId](data-model.md#field-traceid), hex-encoded.
+- "span_id" for [SpanId](data-model.md#field-spanid), hex-encoded.
+- "trace_flags" for [trace flags](data-model.md#field-traceflags), formatted
   according to W3C traceflags format.
 
 All 3 fields are optional (see the [data model](data-model.md) for details of
@@ -432,7 +432,7 @@ Trace id, span id and traceflags SHOULD be recorded via SD-ID "opentelemetry".
 For example:
 
 ```
-[opentelemetry traceid="102981ABCD2901" spanid="abcdef1010" traceflags="01"]
+[opentelemetry trace_id="102981ABCD2901" span_id="abcdef1010" trace_flags="01"]
 ```
 
 ### Plain Text Formats
@@ -441,7 +441,7 @@ The fields should be recorded according to the customary approach used for a
 particular format (e.g. field:value format for LTSV). For example:
 
 ```
-host:192.168.0.1<TAB>traceid:102981ABCD2901<TAB>spanid:abcdef1010<TAB>time:[01/Jan/2010:10:11:23 -0400]<TAB>req:GET /health HTTP/1.0<TAB>status:200
+host:192.168.0.1<TAB>trace_id:102981ABCD2901<TAB>span_id:abcdef1010<TAB>time:[01/Jan/2010:10:11:23 -0400]<TAB>req:GET /health HTTP/1.0<TAB>status:200
 ```
 
 ### JSON Formats
@@ -452,8 +452,8 @@ The fields should be recorded as top-level fields in the JSON structure. For exa
 {
   "timestamp":1581385157.14429,
   "body":"Incoming request",
-  "traceid":"102981ABCD2901",
-  "spanid":"abcdef1010"
+  "trace_id":"102981ABCD2901",
+  "span_id":"abcdef1010"
 }
 ```