[Feat]: Capture LLM Prompts and Responses in Trace Events

[patcher9]

Overview:

This PR places LLM Prompts and Responses in Trace Events rather than the Span Attributes to better align with the OTel GenAI Semantic conventions.

Related #342 (comment)

Changes:

• Prompt is now captured under event name gen_ai.content.prompt with Event attribute name as gen_ai.prompt
• Completions is now captured under event name gen_ai.content.completion with Event attribute name as gen_ai.completion
• Make gen_ai.response.finish_reasons as string[]

"events": [
       {
           "name": "gen_ai.content.prompt",
           "timestamp": "2024-08-01T07:09:15.763840Z",
           "attributes": {
               "gen_ai.prompt": "user: text: How are you?\n"
           }
       },
       {
           "name": "gen_ai.content.completion",
           "timestamp": "2024-08-01T07:09:15.763877Z",
           "attributes": {
               "gen_ai.completion": "I am Amazon Titan, a large language model built by AWS. It is designed to assist you with tasks and answer any questions you may have. How may I help you?"
           }
       }
   ],

Visuals (If applicable):

NA

Checklist:

• PR name follows conventional commit format: [Feat]: ... or [Fix]: ....
• Added visuals for changes (If applicable)
• Checked OpenLIT contribution guidelines