feat: adding vertexai instrumentation support

[darshit-s3]

Description

Adding support for Google Vertex AI instrumentation for methods:

• generateContent
• generateContentStream
• sendMessage
• sendMessageStream

Reference PR for trace-attributes: https://github.com/Scale3-Labs/langtrace-trace-attributes/pull/87

Checklist for adding new integration:

• [ ] Defined APIS in constants folder.
• [ ] Updated SERVICE_PROVIDERS in common.ts
• [ ] Created a folder under instrumentation with the name of the integration with atleast patch.ts and instrumentation.ts files.
• [ ] Added instrumentation in allInstrumentations in init.ts and to the InstrumentationType in types.ts files.
• [ ] Added examples for the new integration in the examples folder.
• [ ] Updated package.json to install new dependencies for devDependencies.
• [ ] Updated the README.md of langtrace-typescript-sdk to include the new integration in the supported integrations table.
• [ ] Updated the README.md of Langtrace's repository to include the new integration in the supported integrations table.
• [ ] Added new integration page to supported integrations in Langtrace Docs