Add basic conformance tests for addEventListener

[Maximiliano-Zeballos]

Describe your change

Add basic conformance tests for addEventListener as described in #1774.

Two tests following the existing pattern used for addContextListener (BasicCL1/BasicCL2):

• BasicAEL1: Verifies addEventListener is callable with a specific event type (userChannelChanged) and returns a valid Listener object with an unsubscribe function.
• BasicAEL2: Verifies the same behavior when passing null as the event type.

Also adds the addEventListener documentation link to apiDocuments.ts.

Related Issue

Resolves #1774

Contributor License Agreement

• I acknowledge that a contributor license agreement is required and that I have one in place or will seek to put one in place ASAP.

Review Checklist

• Issue: If a change was made to the FDC3 Standard, was an issue linked above?
• CHANGELOG: Is a CHANGELOG.md entry included?
• API changes: Does this PR include changes to any of the FDC3 APIs? — No, only conformance tests.

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[kriswest]

The test implementations look fine to me - but we need the definitions also added to the standard's docs at https://github.com/Maximiliano-Zeballos/FDC3/blob/feature/add-event-listener-conformance-test/website/docs/api/conformance/Basic-Tests.md

[kriswest]

Hi @Maximiliano-Zeballos, many thanks for your contribution. Please note that we'll need you to:

• rebase against main
• Add a description of the new case in the docs at: https://github.com/Maximiliano-Zeballos/FDC3/blob/feature/add-event-listener-conformance-test/website/docs/api/conformance/Basic-Tests.md
• add an entry in CHANGELOG.md describing the change