Backport to 3.27: classic_policy_set parameter + example lint fixes (#3385)

[nickanderson]

Backport of #3385 to the 3.27 branch.

Contents

• Doc addition (cherry-picked from Added classic_policy_set parameter to the Create project API endpoint #3385): classic_policy_set parameter on the Create project Build API endpoint.
• Example fixes that the new cfengine dev lint-docs check surfaced and that Added classic_policy_set parameter to the Create project API endpoint #3385 needed to land:
  • example_updating_from_central_hub.markdown — promise attribute separator (; -> ,)
  • policy-writing/policy-style.markdown — same, in two example blocks
  • reference/macros.markdown — replaced placeholder function names (new_function_3_8, old_function_3_15, etc.) with real parsejson('{}') calls; added required arguments to classfiltercsv/readcsv/parseyaml
  • special-variables/this.markdown — promise attribute separator
  • additional-topics/hierarchies.markdown — use => -> usebundle => on a methods promise

cfengine dev lint-docs passes locally on this branch (609/609).

Ticket: ENT-12436