Allow empty values for ee in inventory_source

[kk-at-redhat]

SUMMARY

Added an ability to specify empty value for execution_environment in ansible.controller.inventory_source module.

related #14920

ISSUE TYPE

Bug, Docs Fix or other nominal change

COMPONENT NAME

Collection

ADDITIONAL INFORMATION

Suggested testing:

    - ansible.controller.inventory_source:
        name: "A"
        inventory: "Dynamic A"
      ignore_errors: true

    - ansible.controller.inventory_source:
        name: "A"
        inventory: "Dynamic A"
        execution_environment: "Control Plane Execution Environment"
      ignore_errors: true

    - ansible.controller.inventory_source:
        name: "A"
        inventory: "Dynamic A"
        execution_environment: ""
      ignore_errors: true

    - ansible.controller.inventory_source:
        name: "A"
        inventory: "Dynamic A"
        execution_environment: {}
      ignore_errors: true

    - ansible.controller.inventory_source:
        name: "A"
        inventory: "Dynamic A"
        execution_environment: None
      ignore_errors: true