Improving @brianteeman PR #41122 to extend to field lists.
Thanks to @alikon for the support.

Summary of Changes

Extending the possibility of using the header to list fields as well.
So moving some code from SqlField.php to ListField.php.

Testing Instructions

1. Create a file of type List

2. Create a file of type SQL

3. Create a XML field and add header option

Actual result BEFORE applying this Pull Request

1. you cannot specify the header, so the first value in the list is always selected when creating an article (even if the field is indicated as not required)
2. You can specify the header to obviate the problem described in case 1.

Expected result AFTER applying this Pull Request

1. You may now specify the header

2. The SQL field still works

3. now you can add the header from XML too

Link to documentations

Please select:

• Documentation link for docs.joomla.org: List_form_field_type

• No documentation changes for docs.joomla.org needed

• Pull Request link for manual.joomla.org:

• No documentation changes for manual.joomla.org needed

Note:
Eg of SQL query for SQL Field (you need to create some articles for example from sample data):

SELECT #__content.id AS value, #__content.title AS text
FROM #__content

Eg of XML list field:

	<field
		name="test"
		type="list"
		label="test"
		validate="options"
		header="Please select your option"
		>
		<option value="1">JYES</option>
		<option value="0">JNO</option>
	</field>