Update the client-side testing environment to enable Typescript tests

[jonathonherbert]

What does this change?

Updates the client-side testing environment to enable Typescript tests, adding ts-jest, bumping libraries relating to testing, and tweaking tsconfig.json.

See the commit history for details.

How should a reviewer test this change?

The client-side tests should pass, which should give us confidence that this change is good.

How can success be measured?

Able to write TS tests in #4468 😀

Tested? Documented?

• [ ] locally by committer
• [ ] locally by Guardian reviewer
• [ ] on the Guardian's TEST environment
• [ ] relevant documentation added or amended (if needed)

[github-actions[bot]]

Deploy build 13301 of media-service::grid::all to TEST

All deployment options

• Deploy build 13301 of media-service::grid::all to TEST
• Deploy parts of build 13301 to TEST by previewing it first
• What's on TEST right now?

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From guardian/actions-riff-raff.

[prout-bot]

Seen on image-loader, metadata-editor, thrall, leases, cropper, collections, media-api, kahuna (merged by @jonathonherbert 8 minutes and 26 seconds ago) Please check your changes!

[prout-bot]

Seen on auth, usage (merged by @jonathonherbert 8 minutes and 31 seconds ago) Please check your changes!