DOCS-2686: adding link to contributors section
primer: refactor content migration task
target to clean up primer targets
jobs: use threadpools to reduce overhead in limited situatiosn
content+extension: tweaks to integration and extension system
minor: use processes when possible, and threads only when neededotherwise
steps: passing a more clear error essage when heading text is missing
plugin: removing unused testing function
images: changing generation dependencies
add variable directive for sysvars
sphinx: changing error messages
images+content: fix offline html rendering
shell: better command handling to avoid deadlocks
options: add support for recursive replacements
minor: testing fix for potential deadlock in subprocess executing.
shell: change subprocess use