Missing -mod=${VENDOR_PATH} support for go build

[xenonlcs]

Description:
Missing -mod=${VENDOR_PATH} support for go build. This prevent the use of external private repositories eventually pushed inside the repository

Steps to reproduce the issue:

1. Declare under go.mod a private repository
2. sam build

Observed result:

Build Failed
Error: GoModulesBuilder:Build - Builder Failed: go: ... unknown revision ...

Expected result:
Build without error like env GOOS=linux ARCH=amd64 go build -mod=${VENDOR_PATH} -o ${OUTPUT_PATH} ${TARGET}

Additional environment details (Ex: Windows, Mac, Amazon Linux etc)
No additional environment details