Rename Serverless Workflow to Open Workflow Specification and update related URLs

[riaankleinhans]

cncf/clomonitor#1925

cncf/landscape#5049

[lukaszgryglicki]

Can't work on anything here until I finish super-urgent switchover. Added on my TODO but will take time to get to this.

[krook]

Can't work on anything here until I finish super-urgent switchover. Added on my TODO but will take time to get to this.

No problem. Switchover is the top priority.