Restore formatting and validation behavior after header reordering + add Excel warnings for MEPRAM

[albatalavera]

Changes included

• Updated metadatalab_template.py for MEPRAM.
• Updated the classification_filters list in build_schema_config.json for the MEPRAM project.
• Fixed issues related to the header order change in the Submitting Lab Form.
• Fixed Excel warnings (including for MEPRAM) shown when a value entered in the Excel sheet does not meet the predefined validation criteria.
• Updated appearance in the Submitting Lab Form: Reformatted first column of the METADATA_LAB sheet with gray background and no borders, so it is clearly not meant to be filled in.

PR Checklist

• This comment contains a description of changes (with reason).
• Make sure your code lints (black and flake8).
• CHANGELOG.md is updated.
• README.md is updated (including new tool citations and authors/contributors).

[Aberdur]

LGTM