Move docs repo images to central location

[ericpassmore]

To simplify the install scripts we should move the image locations. This applies to

• docs/01_overview
• docs/02_getting-started
• docs/04_protocol

1) Create a new central directory images under docs 2) Permanently all images from each directory above to docs/images 3) Permanently correct all the markdown files to reference images under path /docs/images 4) During the docsgen build create a new directory under Docusaurus IMG_DIR="${ARG_BUILD_DIR:?}"/devdocs/static/docs/images 5) During the Docusaurus build process copy images from docs github into path listed in 4

[lparisc]

Steps 1,2,3 were done in PRs eosnetworkfoundation/docs#44 and eosnetworkfoundation/docs#46 Steps 4,5 were in PR #87