feat: Add stable exception attributes

resolves #23

model/trace/exception/exception__escaped.json

@@ -0,0 +1,10 @@
+{
+  "key": "exception.escaped",
+  "brief": "SHOULD be set to true if the exception event is recorded at a point where it is known that the exception is escaping the scope of the span.",
+  "type": "boolean",
+  "pii": {
+    "key": "false"
+  },
+  "is_in_otel": true,
+  "example": true
+}

model/trace/exception/exception__stacktrace.json

@@ -0,0 +1,10 @@
+{
+  "key": "exception.stacktrace",
+  "brief": "A stacktrace as a string in the natural representation for the language runtime. The representation is to be determined and documented by each language SIG.",
+  "type": "string",
+  "pii": {
+    "key": "false"
+  },
+  "is_in_otel": true,
+  "example": "Exception in thread \"main\" java.lang.RuntimeException: Test exception\n at com.example.GenerateTrace.methodB(GenerateTrace.java:13)\n at com.example.GenerateTrace.methodA(GenerateTrace.java:9)\n at com.example.GenerateTrace.main(GenerateTrace.java:5)"
+}

model/trace/exception/exception__type.json

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+{
+  "key": "exception.type",
+  "brief": "The type of the exception (its fully-qualified class name, if applicable). The dynamic type of the exception should be preferred over the static type in languages that support it.",
+  "type": "string",
+  "pii": {
+    "key": "false"
+  },
+  "is_in_otel": true,
+  "example": "OSError"
+}