Fix export header for 'Contact ID'

[eileenmcnaughton]

Overview

Fixes

1. the contact id field is exported with the heading 'contact_id' - should be 'Contact ID'
2. code quality issue - we should have metadata defined for all fields but it is missing for
   a few (now one less)

Before

Heading 'contact_id' in export

After

Heading is 'Contact ID'

Technical Details

This is an integer field so it's fine for it to pick up the default length for integers (16 char) instead of the default length for 'I don't know' fields

Comments

[civibot]

(Standard links)

• If this is your first pull-request for CiviCRM, please browse CONTRIBUTING.md for information about the development and testing processes.
• If you are reviewing this pull-request, you may wish to consult the test sites and the Review Standards (long template, short template).

[seamuslee001]

Change makes sense there is good amount of test coverage here merging