Can't use --input-type for exec-file

Describe the problem

There is no way to force subcommand exec-file to use a specific input format with the --input-type.

How to reproduce

$ cat test.yaml
superSecret: ENC[AES256_GCM,data:NtahnsRDqbVULO3sH2jPnw==,iv:caX9CGdMKnDukieQTRfa52QFgNvaf86GALZR67uolX8=,tag:Yni0LEXnSM3BpWhC8lt+MA==,type:str]
sops:
    kms: []
    gcp_kms: []
    azure_kv: []
    lastmodified: '2020-04-14T15:01:38Z'
    mac: ENC[AES256_GCM,data:l2TQUc+PkDKwv+cb1RTo7v8C/4ej5X+byT7DYVowIm13GvGgET05V/R/LadjrZya/aGnSBTUZ87iitiFQvmQmpelxcvoxYOE5fh/Me7uNV7hWRJk8qilHL0zZleApuS32KXK0QVXtgKJ911AQ4tcfeaBz8RdneJb8p31lD7iR3M=,iv:GhLe9YQYP7b2hIP2nzD2wflP+u21t6mhjJldFiM9pYs=,tag:l1IxV/U3T7tU4M4WjGglhA==,type:str]
    pgp:
    -   created_at: '2020-04-14T15:01:37Z'
        enc: |-
            -----BEGIN PGP MESSAGE-----
            <REMOVED>
            -----END PGP MESSAGE-----
        fp: <REMOVED>
    unencrypted_suffix: _unencrypted
    version: 3.5.0

$ cp test.yaml test

$ sops exec-file test.yaml 'cat {}'
superSecret: superSecretValue

$ sops --input-type yaml exec-file test 'cat {}'
Error unmarshalling input json: invalid character 's' looking for beginning of value

Expected behaviour

That the flag --input-type should force sops to decrypt as yaml format.

Start by reproducing the documented exec-file commands and trace how the --input-type flag is handled for that subcommand. Done means using --input-type yaml with an extensionless input decrypts successfully instead of attempting JSON unmarshalling.