feat: add backend for METS with Google Books profile (#1989)

* add backend for METS with Google Books profile

Signed-off-by: Michele Dolfi <dol@zurich.ibm.com>

* Fixes for cell indexing

Signed-off-by: Christoph Auer <cau@zurich.ibm.com>

* use HTMLParser and add options from CLI

Signed-off-by: Michele Dolfi <dol@zurich.ibm.com>

* fix typing and unloading

Signed-off-by: Michele Dolfi <dol@zurich.ibm.com>

* restore guess format

Signed-off-by: Michele Dolfi <dol@zurich.ibm.com>

* rename inputformat

Signed-off-by: Michele Dolfi <dol@zurich.ibm.com>

* use PdfDocumentBackend

Signed-off-by: Michele Dolfi <dol@zurich.ibm.com>

* use test file from test folder (still missing)

Signed-off-by: Michele Dolfi <dol@zurich.ibm.com>

* add test file

Signed-off-by: Michele Dolfi <dol@zurich.ibm.com>

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Signed-off-by: Michele Dolfi <dol@zurich.ibm.com>
Signed-off-by: Christoph Auer <cau@zurich.ibm.com>
Co-authored-by: Christoph Auer <cau@zurich.ibm.com>