feat(threatComposer): make cdn configurable via VS Code settings

[ellgregs]

Problem

Users are unable to utilise a customised self-hosted ide-specific threat composer deployment within vs-code unless within a private network with customised dns resolution, due to the hardcoded URL for the ide-threat-composer editor resources.

Benefit of leveraging a self-hosted deployment of threat composer is users can include customised threat/mitigation packs - outlined here.

Solution

Added a configurable VS-Code setting aws.threatComposer.cdn that allows users to override the default cdn value 'https://ide-toolkits.threat-composer.aws.dev'.

Testing

Change is minimal: 2 files changed

Caveats

Does require the users self-hosted version to update the content security policy in their deployment of the ide variant of threat-composesr but that seems a reasonable expectation.

sed -i -e `s|https://ide-toolkits.threat-composer.aws.dev|<cdn>/|g` ./threat-composer/packages/threat-composer/public/index.html
sed -i -e `s|data:|data: <cdn>/|g` ./threat-composer/packages/threat-composer/public/index.html

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[amazon-inspector-ohio]

⏳ I'm reviewing this pull request for security vulnerabilities and code quality issues. I'll provide an update when I'm done

[amazon-inspector-ohio]

✅ I finished the code review, and didn't find any security or code quality issues.

[github-actions]

• This pull request modifies code in src/* but no tests were added/updated.
  • Confirm whether tests should be added or ensure the PR description explains why tests are not required.

[ellgregs]

Hey @bijinai, I've added a setting to be able to use a self-hosted version of threat-composer within vs-code. Since you've previously worked on this I'd appreciate your input when you have a chance. Thanks

[bijinai]

The change look good