Koa.3 and Lilac.master

Steps for open-release/koa.3 tag:

@Ned Batchelder (Deactivated) apply the recent Django 2.2.20 security patch to koa.master
@Ned Batchelder (Deactivated) add Adolfo to open-release team
@Former user (Deleted) makes sure there are no relevant incomplete tickets with the koa.3 milestone
@Former user (Deleted) make the k.3rc1.1 branch on koa.master
@Former user (Deleted) test the rc
@Former user (Deleted) make the koa.3 tag
@Former user (Deleted) ping Régis
@Former user (Deleted) update the relevant doc pages (make PR)

Steps for open-release/lilac.master branch

@Ned Batchelder (Deactivated) check the set of repos for Lilac, and keep open-release team up to date
@Former user (Deleted) make the lilac.master branch
@Former user (Deleted) update the RELEASE_LINE constant
@Former user (Deleted) update the transifex configuration
@Ned Batchelder (Deactivated) update Django to 2.2.20 (it’s a mix of 17, 19, and 20 now)
@Ned Batchelder (Deactivated) update the docs for the lilac branch
@Ned Batchelder (Deactivated) update the edx-platform and configuration pull request templates to mention lilac.
@Ned Batchelder (Deactivated) announce lilac.master inside edX. Mention the PR template change.
@Ned Batchelder (Deactivated) remove Adolfo from open-release team
@Former user (Deleted) announce the lilac.master branch within BTR. Explain that it’s only for testing, not production.