Do not fail a convert for "Unrecognized element"

[suntong]

Is your feature request related to a problem?

As jmeter-to-k6 will not be able to work on all JMeter files, I think it is a good idea not to fail a convert for "Unrecognized element", for e.g., #49.

Describe the solution you'd like

Turn those unrecognized elements into comments.
For e.g., #49, just add a comment line /* TODO: JDBCSampler */, where the JDBCSampler step should be and move on. Maybe that's the only 1% failure of the script and the rest of 99% is fine.

Another example:

(node:8140) UnhandledPromiseRejectionWarning: Error: Unrecognized element: kg.apc.jmeter.samplers.DummySampler
    at element (/usr/lib/node_modules/jmeter-to-k6/src/element.js:61:11)

Describe alternatives you've considered

There might be alternatives, but the point is, for the case of only 1% the script failed the rest of 99% fine part, not failing a convert process might be the cheapest choice, among all alternative cases.

[ahosking]

Another:
(node:4413) UnhandledPromiseRejectionWarning: Error: Unrecognized element: UserParameters
User Parameters are not supported.