feat: improve error message when generating fromTemplate #1728

[Aditya-twd]

Closes #1728

This PR improves error messages when asyncapi generate fromTemplate fails while working with templates.

Changes

• Improve error handling in GeneratorService.generate so that generator failures are surfaced as clearer, user‑friendly messages in the CLI.
• Add a specific message when a template cannot be found or installed from the registry (for example, wrong name, missing scope, or 404‑like situations).
• Handle cases where the template directory is missing or corrupted (for example, ENOENT on the template path) and explain that the template installation or local folder is invalid.
• Clarify messages related to template–generator version incompatibility so users understand that a different generator or template version is required.
• Provide more informative hints for network or registry‑related failures that occur while resolving or installing a template (for example, unreachable registry or misconfigured URL).

A screenshot of the core issue being resolved

--

Notes

The generic banner text (Something went wrong / Generation failed) is still printed by the existing CLI UI layer before the detailed Generator Error: ... message. This PR focuses on improving the generator error details and template‑related messages.

Manual testing

Manual testing is done
In order to see the issue this PR proposes to solve, follow these steps:

In the CLI repository, with a valid asyncapi.yaml in the current directory:
Run commands:

1. Non‑existent template name (template cannot be found/installed)

---> asyncapi generate fromTemplate ./asyncapi.yaml not-installed-template -o /tmp/out1

2. Unscoped template name (should be @asyncapi/html-template)

---> asyncapi generate fromTemplate ./asyncapi.yaml html-template -o /tmp/out2

3. Valid scoped template but unreachable/invalid registry URL (network/registry error)

---> asyncapi generate fromTemplate ./asyncapi.yaml @asyncapi/html-template --registry-url https://fake-registry.example.com -o /tmp/out3

[changeset-bot]

🦋 Changeset detected

Latest commit: 75519e5

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@asyncapi/cli	Patch

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[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[Souvikns]

@Shurtu-gal are the /src/errors/ meant to be used in the services classes. If it is then maybe move this logic to the dedicated error classes.