feat(gen_ai): Add details to request messages description (#14831)

Add more details to `gen_ai.request.messages` span description.

- Relates to getsentry/sentry-conventions#122

Author: ArthurKnaus

develop-docs/sdk/telemetry/traces/modules/ai-agents.mdx

@@ -46,7 +46,7 @@ Additional attributes on the span:
 | `gen_ai.usage.total_tokens`            | int    | optional          | The total number of tokens used to process the prompt. (input and output)               | `190`                                                                                                             |
 
 - **[0]:** Span attributes only allow primitive data types (like `int`, `float`, `boolean`, `string`). This means you need to use a stringified version of a list of dictionaries. Do NOT set `[{"foo": "bar"}]` but rather the string `"[{\"foo\": \"bar\"}]"`.
-- **[1]:** Each message item uses the format `{role:"", content:""}`. The `role` can be `"user"`, `"assistant"`, or `"system"`. The `content` can be either a string or a list of dictionaries.
+- **[1]:** Each message item uses the format `{role:"", content:""}`. The `role` must be `"user"`, `"assistant"`, `"tool"`, or `"system"`. For messages of the role `tool`, the `content` can be a string or an arbitrary object with information about the tool call. For other messages the `content` can be either a string or a list of dictionaries in the format `{type: "text", text:"..."}`.
 
 ### AI Client Span
 
@@ -76,7 +76,7 @@ Additional attributes on the span:
 | `gen_ai.usage.total_tokens`            | int    | optional          | The total number of tokens used to process the prompt. (input and output)               | `190`                                                                                                             |
 
 - **[0]:** Span attributes only allow primitive data types. This means you need to use a stringified version of a list of dictionaries. Do NOT set `[{"foo": "bar"}]` but rather the string `"[{\"foo\": \"bar\"}]"`.
-- **[1]:** Each message item uses the format `{role:"", content:""}`. The `role` can be `"user"`, `"assistant"`, or `"system"`. The `content` can be either a string or a list of dictionaries.
+- **[1]:** Each message item uses the format `{role:"", content:""}`. The `role` must be `"user"`, `"assistant"`, `"tool"`, or `"system"`. For messages of the role `tool`, the `content` can be a string or an arbitrary object with information about the tool call. For other messages the `content` can be either a string or a list of dictionaries in the format `{type: "text", text:"..."}`.
 
 ### Execute Tool Span