Handle shell-quoted environment varaibles

[alialkhalidi]

When converting string values for environment variables of type bool or numbers, startcmd fails to parse shell-quoted values. For example: when setting EDV_DATABASE_TIMEOUT="60", startcmd fails with:
Error: failed to parse timeout "60": strconv.Atoi: parsing "\"60\"": invalid syntax
making the environment variables of less use, and leaving only the option of passing command parameters for these configurables.
This can either be handle here or in https://github.com/trustbloc/edge-core/blob/main/pkg/utils/cmd/util.go