feat: end support for Node.js 14.x

[naotama2002]

Is your feature request related to a problem? Please describe.
Node.js tests are failing because aws-sdk-js-3 (@aws-sdk/client-cloudformation), on which examples/minimal/ depends, no longer supports Node.js 14
ex. https://github.com/floydspace/serverless-esbuild/pull/537/checks

The cause is the end of support for Node.js 14.x in aws-sdk-js-3 issue #6034.
Therefore, since the release of aws-sdk-js-3 v3.567.0 which includes #6034, tests for Node.js 14 will fail.

Describe the solution you'd like
End support for Node.js 14.x.

Describe alternatives you've considered
"I have no ideas.

Additional context
Since Node.js 14 is not listed in the supported runtimes, I think supporting Node.js 16 and 18 is sufficient.

• https://docs.aws.amazon.com/lambda/latest/dg/lambda-runtimes.html