perf(#600): drop support for Node versions < 18

[sugat009]

Description

Dropping support for NodeJS < 18.

medic/cht-conf#600

Code review items

• Readable: Concise, well named, follows the style guide, documented if necessary.
• Documented: Configuration and user documentation on cht-docs
• Tested: Unit and/or integration tests where appropriate
• Backwards compatible: Works with existing data and configuration. Any breaking changes documented in the release notes.

License

The software is provided under AGPL-3.0. Contributions to this project are accepted under the same license.

[garethbowen]

@sugat009 I've changed the branch protections so only Node 18 and 20 are required, so this is good to merge. Remember to use the BREAKING CHANGE comment in the description to force a major release.

[medic-ci]

:tada: This PR is included in version 4.0.0 :tada:

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

Your semantic-release bot :package::rocket: