pg_walinspect: Add pg_get_wal_fpi_info()

pg_walinspect: Add pg_get_wal_fpi_info()

This function is able to extract the full page images from a range of
records, specified as of input arguments start_lsn and end_lsn.  Like
the other functions of this module, an error is returned if using LSNs
that do not reflect real system values.  All the FPIs stored in a single
record are extracted.

The module's version is bumped to 1.1.

Author: Bharath Rupireddy
Reviewed-by: Bertrand Drouvot
Discussion: https://postgr.es/m/CALj2ACVCcvzd7WiWvD=6_7NBvVB_r6G0EGSxL4F8vosAi6Se4g@mail.gmail.com