Add GB-LAESTAB List

[R2ZER0]

In 360 Giving some Educational Institutions are using GB-LAESTAB Org-IDs.

This seems to be a "Local Authority + Establishment" combined code which, as far as i can tell, is another identifier for "Educational Establishments" in addition to GB-EDU and GB-UKPRN.

If you go to: https://get-information-schools.service.gov.uk/Search?SelectedTab=Establishments
and select "Search by Name or Reference number", the help text says:

Name or reference identification number

Enter the establishment's name or one of the following reference identification numbers associated with the establishment:

• URN (unique reference number)
• LAESTAB (local authority establishment number)
• UKPRN (UK provider reference number)

Also see: https://www.understandingsociety.ac.uk/documentation/linked-data/education-data-linkage/npd-variables/census/laestab/

[IsabelBirds]

@R2ZER0 I think this issue should be here https://github.com/org-id/register/issues