Coverage gaps in `opentelemetry-instrumentation-google-genai` instrumentations

[DylanRussell]

Using this to track some gaps as I go about monkey patching various APIs as part of the openinference donation stuff..

Gaps:
A generic way for the user to provide attributes that make it into the span.. We use a ContextVar to do this for the GenerateContent method, and could do the same for the other APIs..

Embeddings:

• We could allow capturing various EmbedContentConfig in attributes the same way we do GenerateContentConfig in the generate_content instrumentation.
• Openinference captures the actual raw embeddings in their instrumentation -- that seems too big to put into an attribute..

Interactions:

• Execute tool span, and tool definitions.
• Need to capture interaction ID.
• Expand input / output messages to capture all inputs / outputs -- the SDK accepts so many different types