README: Add header warning of migration to monorepo

Website hostname change: kurento.org -> kurento.openvidu.io

Use "6.12.0" everywhere as example version number

bug_report: clarify that only debug logs should go in triple backuotes

bug_report: fix wrong ordering of header sections

bug_report: clarify that the template is mandatory

Update URLs to latest Kurento doc versions in ReadTheDocs

new-issue: cancel when state != open instead of state == closed

new-issue: edit from check-template, add full workflow

bug_report: align comments to their final appearance (not monospaced)

bug_report: reword the section asking for command outputs and backquotes

Enforce issue template: link to raw issue template file

Enforce issue template: relax conditions, don't require an [X]

bug_report: link to the new issue chooser screen

Enforce issue template: enable with a single-line trigger pattern