create flag to allow skipping the ci build
create flag to allow skipping the ci build

Add a commitFlag that allows the user to skip CI

refs DE-192
flag = none

[canvas-builds-refspec=618e43174bc58f54905421e18b212d96f9eb0b95]

test plan:
- Ensure the build is skipped using the flag
- Ensure a code-review -2 is assigned if the skip ci flag is enabled
- Ensure the build is executed and passes when the flag is removed

Change-Id: I5c57d9959e4650ccd42578672f4df38ca9abce34
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/256070
Reviewed-by: Aaron Ogata <11ccf682c06d1508642f943a3962a1c3d00b8e44@instructure.com>
Tested-by: Service Cloud Jenkins <9144042a601061f88f1e1d7a1753ea3e2972119d@instructure.com>
QA-Review: Andrea Cirulli <b4e55ef5ee4bae8ad31f7c81009bfc0af1714a1f@instructure.com>
Product-Review: Andrea Cirulli <b4e55ef5ee4bae8ad31f7c81009bfc0af1714a1f@instructure.com>

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