Update to the CircleCI config

[echoesactiii]

Status

Note: this repository will not have CircleCI Slack notifications until either this is merged, or infra-side changes are reverted. in the case the latter is needed please ping me on slack directly!

Part of https://github.com/freedomofpress/infrastructure/issues/3225

Description of Changes

Changes proposed in this pull request: this updates the CircleCI config to the latest version, enables the Slack orb, adds a step to call Slack on a failure, and then maps that to each job in the workflow.

this repository has been using a legacy CircleCI integration that is no longer supported, and this brings it up to date with the current guidance for integrationg CircleCI and Slack.

Testing

easiest thing to do would be to do something that would cause a CI failure and make sure the notification pops into Slack. that would have to be done in this branch (or a child) unless this is otherwise merged first.

Deployment

deploys on merge, no effect outside of circleCI

Choose one of the following:

• These changes do not require documentation

[zenmonkeykstop]

Jobs are passing as expected, so I'm ok with merging as-is - one thing that would have to be done post-merge tho is to fix up the static analysis job, either renaming it to match the required job in the GH repo settings, or updating repo settings to use the new name.

update: oh wait, merging will be blocked until that's changed. Grrr.