build(docker-build): optimize the docker build process

[ellerbrock]

hello @tjamet,

like discussed in #4154 i updated the dockerfile for faster build times.

it's always a pleasure to work together with other smart people on open source project and end up with something better then before.

cheers maik

[ellerbrock]

i added a .dockerignore file like mentioned in docker best practices and excluded some folders to optimize the build time a bit.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. The resources of the Hugo team are limited, and so we are asking for your help.
If this is a bug and you can still reproduce this error on the master branch, please reply with all of the information you have about it in order to keep the issue open.
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This issue will automatically be closed in the near future if no further activity occurs. Thank you for all your contributions.

[anthonyfok]

This pull request from December 2017 was superseded by PR #4518 in March 2018. Many thanks to @ellerbrock and @skoblenick for your group effort in improving Dockerfile!

[github-actions]

This pull request has been automatically locked since there has not been any recent activity after it was closed. Please open a new issue for related bugs.