Reading variables from variable type file for cicd pipeline

We have a scenario where we want to read variables from a file(not gitlab.ci file) and when we trigger/run pipeline manually, it should read the variables from file and give the options in the UI to select one.
Example:
file.txt
variables:
DEPLOY_ENV:
value: “stage”
options:
- “production”
- “stage”
- “test”

when i trigger pipeline from UI and select the variable , i should get dropdown to select one of those values and continue the pipeline.
Currently not finding an option for variable type as file.