chore: changing node support level to min v18

[nicholasgriffintn]

Resolves #413

Description:

As a result of the security support ending for Node v16 on September 11th, this PR sets the minimum supported version for Node to version 18.

After the release of this change, SQS Consumer will only support Node versions 18 and 20.

Type of change:

• [ ] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [x] Breaking change (fix or feature that would cause existing functionality to change)

Why is this change required?:

To ensure that we keep this library secure and at the latest expectations, we only support Node versions that are actively or security release supported.

Code changes:

• Updated the README
• Updated the workflows to remove Node 16
• Updated the Node version in package.json

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[codeclimate[bot]]

Code Climate has analyzed commit a7d01795 and detected 0 issues on this pull request.

The test coverage on the diff in this pull request is 100.0% (80% is the threshold).

This pull request will bring the total coverage in the repository to 96.9% (0.0% change).

View more on Code Climate.