Include more request configuration options into the span attributes for the Google GenAI SDK instrumentation

[michaelsafyan]

Description

Improves the comprehensiveness and uniformity of reporting span-level attributes for Google GenAI SDK operations.

This essentially dumps all of the configuration options into span attributes, with a vendor-specific prefix. The subset of request options that are defined in OTel Semantic Conventions are then renamed to match conventions.

In service of the above, this change also:

1. Adds a flatten_dict util used to generate the span attributes.
2. Adds tests to more fully cover the set of attributes that are included.

Type of change

• New feature (non-breaking change which adds functionality)

How Has This Been Tested?

Added more integration tests, covering the relevant changes.

Does This PR Require a Core Repo Change?

• No.

Checklist:

• Followed the style guidelines of this project
• Changelogs have been updated
• Unit tests have been added
• Documentation has been updated

[michaelsafyan]

Friendly ping. Is it possible to get this reviewed?

[xrmx]

I approved the PR because I think this would be helpful for you to move forward but would be nice to add a google genai specific section to the genai semantic conventions with these attributes you are exporting. Now it's really opaque and we don't have assertions on what we are actually exporting.