Backport 1.4.0 changes to develop

[conorsch]

Status

Ready for review.

Description of Changes

Towards #5289

Changes proposed in this pull request:

• backports 1.4.0 release commits from release/1.4.0 branch to develop
• updates version info 1.4.0 -> 1.5.0~rc1

See https://docs.securedrop.org/en/master/development/release_management.html#release-process for reference. We only had one rc1, so there's not much in this branch. As part of review, confirm that no commits were missed from the release/1.4.0 that should be included here.

Testing

How should the reviewer test this PR?
Write out any special testing steps here.

Deployment

Any special considerations for deployment? Consider both:

1. Upgrading existing production instances.
2. New installs.

Checklist

If you made changes to the server application code:

• Linting (make lint) and tests (make test) pass in the development container

If you made changes to securedrop-admin:

• Linting and tests (make -C admin test) pass in the admin development container

If you made changes to the system configuration:

• Configuration tests pass

If you made non-trivial code changes:

• I have written a test plan and validated it for this PR

If you made changes to documentation:

• Doc linting (make docs-lint) passed locally

If you added or updated a code dependency:

Choose one of the following:

• I have performed a diff review and pasted the contents to the packaging wiki
• I would like someone else to do the diff review

[sssoleileraaa]

• correct commits were cherry-picked:

• efd1121
• 93f4259

These commits match what you see when you run:
git log --pretty=oneline changelog.md since the last post-release commit for 1.3.0

• post-release version bump from 1.4.0 to 1.5.0~rc1

[eloquence]

Changes LGTM as well, kicked CI.

[kushaldas]

Kicked CI again sometime ago.