feat: support multiple --env-file in ComposeConfig #382

Job	Run time
Minimum Supported Rust Version	1m 18s
Docker Integration Tests	4m 9s
Documentation	38s
Security Audit	33s
Dependency Management	28s
Test Suite (ubuntu-latest, stable)	2m 44s
Test Suite (ubuntu-latest, beta)	2m 32s
Test Suite (windows-latest, stable)	9m 39s
Test Suite (macos-latest, stable)	4m 18s
	26m 19s

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