Create Metadata change directory - and populate it with latest significant metadata change

[salichon]

• Create the relevant space for this metadata documentation
• Populate it with the most significant metadata change (response correction) recently implemented
• Place holder for future noticeable correction (if so)
• Add documentation about https://github.com/GeoNet/delta/pull/1226

[salichon]

• List of the station and sites affected by the Obsidian response change:

• date and time of Obsidian 4X response change 2022-02-17 02:00:00 UTC

[salichon]

Doco PR for Obsidian meta:https://github.com/GeoNet/help/pull/95

[salichon]

doc available at https://github.com/GeoNet/help/tree/main/metadata-changes