WAL archive catalog

[gsmolk]

Currently, there is no way for user to get information about the state of WAL archive.

[gsmolk]

The work is done at https://github.com/postgrespro/pg_probackup/tree/pbckp-83

[gsmolk]

Example

ARCHIVE INSTANCE 'master'
==============================================================================================================
 TLI  Parent TLI  Switchpoint  Min Segno         Max Segno         N files  Size    Zratio  Status  N backups 
==============================================================================================================
 1    0           0/0          0000000000000001  0000000000000008  8        5289kB  25.00   OK      2

[gsmolk]

Do we need ...

1. separate command for viewing WAL archive? E.g. 'show-archive'.
2. interface for WAL management? E.g 'delete specific range of WAL or whole timeline'.

[gsmolk]

Merged