feat: add support for alter schema drop vector index

[antas-marcin]

Summary

• Add delete_vector_index(vector_name) method to collection config, allowing users to drop a named vector's index via DELETE /v1/schema/{className}/vectors/{vectorIndexName}/index
• Follows the same pattern as the existing delete_property_index method
• Includes both sync and async type stubs

Closes #1990

[orca-security-eu]

Orca Security Scan Summary

Status	Check	Issues by priority
Passed	Infrastructure as Code	0   0   0   0	View in Orca
Passed	SAST	0   0   0   0	View in Orca
Passed	Secrets	0   0   0   0	View in Orca
Passed	Vulnerabilities	0   0   0   0	View in Orca