[19.03 backport] assorted documentation changes

[thaJeztah]

backports of:

• Docs: add note about management commands targeting a manager #1590 Docs: add note about management commands targeting a manager
  • minor conflict in stack_deploy.md due to Remove experimental "deploy" from "dab" files #2216 not being in 19.03
• Update service_create.md #2054 Update service_create.md
• Fixing some links and deleting an older page reference #2202 Fixing some links and deleting an older page reference
• Add docs for proxy configuration in config.json #2224 Add docs for proxy configuration in config.json
  • taking the docs changes from Add ALL_PROXY to build-arg whitelist moby/moby#37125. Setting proxy-configuration in config.json was added in commit 35f1e30 (Allow Proxy Configuration in config.json #93) (docker 17.07), but never found its way to the documentation.
• Change example networks #2231 Change example networks

[silvin-lubecki]

LGTM