Fastlane: Use custom keychain - CU-862k3ha8p

Notable changes:

• Uses a custom keychain (fastlane.keychain) instead of default keychain (login.keychain)
• Specify version of Fastfile to use with FASTFILE_VERSION

Testing:

To test the change, used a cut down version of the pipeline that only does the build stage. See an example here.

Used two projects on which change was tested:

• liljaiceland11-269498-react-native - doesn't use custom certificate
• innovxlsolutionsllp-150753-react-native - uses custom certificate

Test case	Pipeline
First run - expect to create keychain during this run	https://gitlab.builder.ai/clientprojects/assembler_projects/prd/innovxlsolutionsllp-150753-react-native/-/jobs/19717978
Second run on the same runner - expect for keychain to be deleted and recreated	https://gitlab.builder.ai/clientprojects/assembler_projects/prd/innovxlsolutionsllp-150753-react-native/-/jobs/19720433
First run on non custom certificate project	https://gitlab.builder.ai/clientprojects/assembler_projects/prd/liljaiceland11-269498-react-native/-/jobs/19788846
Second run on non custom certificate project	https://gitlab.builder.ai/clientprojects/assembler_projects/prd/liljaiceland11-269498-react-native/-/jobs/19794079
Full pipeline run	https://gitlab.builder.ai/clientprojects/assembler_projects/prd/innovxlsolutionsllp-150753-react-native/-/pipelines/3385161