Add type validation to inputs

What does this MR do and why?

This MR adds type validation to CI inputs. The available types are string, number, and boolean. Inputs without an explicit type are type string by default, which preserves the existing un-typed behavior.

Screenshots or screen recordings

Included template

This CI configuration requires 3 inputs, one from each of the possible types.

Error messages

This configuration passes a number to test_input when a string is expected.

This configuration passes a string to multiple when a number is expected.

This configuration passes a string to run_job when a boolean is expected.

This configuration passes incorrect values to all 3 inputs, so an error message is displayed for each

Working configuration

This configuration passes correct values to all 3 inputs

The included job runs successfully, with this output

How to set up and validate locally

1. In a project, create a file included.yml with the following configuration:

   spec:
       inputs:
           test_input:
               type: string
           multiple:
               type: number
           run_job:
               type: boolean
   
   ---
   
   included_job:
       script:
           - echo "`expr 2 \* $[[ inputs.multiple ]]`"
           - echo $[[ inputs.test_input ]]
           - if [ $[[ inputs.run_job ]] = true ] ; then
               echo 'run_job input is true!' ;
             fi

2. In the CI editor, add the following config

   include:
       local: included.yml  
       inputs:  
           test_input: STRING_HERE 
           multiple: NUMBER_HERE
           run_job: BOOLEAN_HERE

3. Give invalid values to the inputs and see that you get accurate error messages
4. Give valid values to the inputs and save the configuration
5. Run a pipeline and see that included_job runs successfully

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #390458 (closed)