Change engine name

[ArshiaDadras]

This pull request includes updates to rename an engine identifier across multiple services and a version bump for the application. The most important changes involve replacing Giraffe with Zarrafe in the EtaEngine and MatrixEngine constants and their corresponding string representations, as well as updating the application version.

Engine Identifier Updates:

• services/eta/call_options.go: Replaced EtaEngineGiraffe with EtaEngineZarrafe in the const block and updated the String() method to return "zarrafe" instead of "giraffe". [1] [2]
• services/matrix/call_options.go: Replaced MatrixEngineGiraffe with MatrixEngineZarrafe in the const block and updated the String() method to return "zarrafe" instead of "giraffe". [1] [2]

Version Update:

• version/version.go: Updated the application version from v0.9.19 to v0.9.20.

[ArshiaDadras]

@SamMHD This is your birthday gift!