Changed timing of check from before to after message wrapping

[chiaramapellimt]

What

The schema validation is now running on the complete outbound message (including the outer RCMR_IN030000UK06/UK07 wrapper) rather than just the inner EhrExtract content.
Related ticket is NIAD-3462

Why

Previously the validation was always failing silently because it was validating the wrong thing.

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Internal change (non-breaking change with no effect on the functionality affecting end users)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist:

• I have performed a self-review of my code
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• I have updated the Changelog with details of my change in the UNRELEASED section if this change will affect end users

[github-actions]

Looks good. All 4 mutations in this change were killed.

class	surviving	killed
💯uk.nhs.adaptors.gp2gp.gpc.StructuredRecordMappingService	0	4

See https://pitest.org

• Arcmutate licence valid until 2028-03-02 (yyyy/mm/dd) (non-commercial use only)
• Project uses Spring, but the Arcmutate Spring plugin is not present.