fix: Handle BYO Embeddings (#4387)

[erichare]

This PR fixes #4387 by passing in the optional embedding provider key properly

[codspeed-hq]

CodSpeed Performance Report

Merging #4410 will degrade performances by 16.78%

_{Comparing bugfix-astradb-byoe (397d197) with main (01de9ef)}

Summary

⚡ 1 improvements
❌ 3 regressions
✅ 12 untouched benchmarks

⚠️ Please fix the performance issues or acknowledge them on CodSpeed.

Benchmarks breakdown

	Benchmark	main	bugfix-astradb-byoe	Change
⚡	test_load_flows	1,188.5 µs	875.1 µs	+35.82%
❌	test_invalid_run_with_input_type_chat	14.9 ms	16.7 ms	-10.39%
❌	test_successful_run_with_input_type_any	452.3 ms	528.5 ms	-14.41%
❌	test_successful_run_with_output_type_debug	375.6 ms	451.4 ms	-16.78%

[Cristhianzl]

lgtm