Stop validating `default` CI input type in Entry

What does this MR do and why?

CI inputs can be 3 types - string, number, or boolean. Input default value types are validated to conform to the type of the input. Type validation for the default value is done correctly in the Interpolation::Inputs classes

However, we also validate the type of the default keyword in the Header::Input Entry class. This validation is broken because it only allows string values for default. Since there is no existing validator to type check for [String | Number | Boolean], this MR removes the default validation from Header::Input.

Also - in the future we plan to move the default value validations from Interpolation::Inputs to Header::Input. I considered doing that work now, but it would take much longer and I think it's more important that we have an expedient fix for this bug

Changelog: fixed

How to set up and validate locally

With this component;

# project: root/component-project
# file: templates/my_component.yml

spec:
  inputs:
    port:
      type: number
      default: 3000
    allow_failure:
      type: boolean
      default: true
---
test_job:
  script: ls

In the CI editor, include this component;

include:
  - component: gdk.test:3000/root/component-project/my_component@main

test:
  script: echo "Hello"

Before this MR:

After this MR:

Valid!

---

Also, we still have the invalid default type error.

# project: root/component-project
# file: templates/my_component.yml

spec:
  inputs:
    port:
      type: number
      default: []
---
test_job:
  script: ls

In the CI editor, include this component;

include:
  - component: gdk.test:3000/root/component-project/my_component@main

test:
  script: echo "Hello"

Before this MR:

After this MR:

See that you still get an "invalid default type" error message.

MR acceptance checklist

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

Related to #429647 (closed)