voltha-docs: sphinx template substitution seems to have stopped working

https://gerrit.opencord.org/c/voltha-docs/+/35230

https://jenkins.opencord.org/job/verify_voltha-docs_unit-test/534/consoleFull

Release notes generation for voltha_2.12 was working fine a while back (while being written).

Not sure where this behavior came from.

No interpreter or python module upgrades to date.

Only substantial changes have been peripheral, migrating dns and orgs from ONF to Linux Foundation.

% make linkcheck

14:15:58 (release_notes/voltha_2.12: line   44) broken |jira-opencord|/VOL-4436 

14:15:58 (release_notes/voltha_2.12: line  245) broken    |mvn-api|-api/2.11.0 - 
14:15:58 (release_notes/voltha_2.12: line  246) broken    |mvn-api|/2.11.0 - 
14:15:58 (release_notes/voltha_2.12: line  300) broken    |mvn-olt|-api/5.2.6 - 
14:15:58 (release_notes/voltha_2.12: line  112) broken    |jira-opencord|/VOL-5219 - 
14:15:58 (release_notes/voltha_2.12: line  244) broken    |mvn-aaa|-api/2.11.0 - 

URLs in the version table are created by string substitution (sphinx logic).
Template is defined at the bottom of the rst file.

Pages were rendering properly before, not sure what may have changed.