[datadog_rum_retention_filter] Support decimal sample_rate values

[davis-rule]

Summary

Updates the sample_rate field for RUM retention filters to support decimal values (e.g., 50.5%). This enables users to configure more precise retention filter sample rates.

Changes:

• Resource: Update schema from Int64Attribute to Float64Attribute
• Data source: Update schema type from Int64Type to Float64Type
• Tests: Add test case for decimal sample_rate (50.5)

Dependencies

⚠️ This PR is blocked until the following are completed:

1. OpenAPI spec PR merged: https://github.com/DataDog/datadog-api-spec/pull/4695
2. datadog-api-client-go SDK regenerated with new float type

Once the SDK is updated, this PR will need:

make update-go-client  # Pull new SDK
make docs              # Regenerate documentation

Related

• Jira: https://datadoghq.atlassian.net/browse/RUM-13145
• rum-config PR: https://github.com/DataDog/dd-source/pull/316909
• rum-api PR: https://github.com/DataDog/logs-backend/pull/118888
• OpenAPI spec PR: https://github.com/DataDog/datadog-api-spec/pull/4695

Test plan

• Wait for SDK update
• Run make update-go-client
• Verify build passes
• Run tests with RECORD=true to capture new cassettes
• Verify decimal values work end-to-end