INFRA-8460 Initial kabuild container (#65)

Note: Naming and location of this container is not final.
It may be better located in webapp. Nevertheless, it is
useful now in several ways.

* Try to do everything that linux-setup.sh does
* Enough debug tools that this container is useful for debugging things

Issue: https://khanacademy.atlassian.net/browse/INFRA-8460

Test plan:

Run the following commands:
- make build
- make run_dirty

Check that ~/khan contains local ~/khan and that git works.
This is likely very slow on a mac, so be careful.

Ideally, try a clean checkout of webapp somewhere followed by
"make deps". This is probably best tested on a linux machine.

INFRA-8460 Cleanup and test likely targets

Add a README.md file and Makefile with common tasks.
Remove unused k8 manifests.

Issue: https://khanacademy.atlassian.net/browse/INFRA-8460

Test plan:

Run the following commands:
- make build
- make run_dirty

Check that ~/khan contains local ~/khan and that git works.
This is likely very slow on a mac, so be careful.

Ideally, try a clean checkout of webapp somewhere followed by
"make deps". This is probably best tested on a linux machine.

Also test "make run"

INFRA-8460 Initial kabuild container

* Try to do everything that linux-setup.sh does
* Enough debug tools that this container is useful for debugging things

Issue: https://khanacademy.atlassian.net/browse/INFRA-8460

Test plan:

Build everything by running "skaffold build"

Map ssh identity and location to checkout code into (/data),
checkout code and successfully run make deps.

docker run -it \
  -v ~/data:/data \
  -v ~/.ssh/id_rsa:/home/kbuild/.ssh/id_rsa \
  <image-name>