[Security Solution] EASE Value Report Export PDF Fix

[stephmilovic]

Summary

The domtoimage.toPng method caused the following CSP related errors when attempting to export PDF from the EASE Value Report:

core.entry.js:1 domtoimage: Error while reading CSS rules from https://kibana.estccdn.com/29ed9d1b5e7a/ui/legacy_light_theme.min.css SecurityError: Failed to read the 'cssRules' property from 'CSSStyleSheet': Cannot access rules

kbn-ui-shared-deps-npm.dll.js:1 Refused to connect to 'data:image/png;base64,.....' because it violates the following Content Security Policy directive: "connect-src 'self' https:".

Using domtoimage.toBlob fixes the error.
#222757

To test

There is an identical branch with a deployment being used for demo. Test the export on that branch to ensure export pdf works on cloud serverless instance (previously we only tested locally, leading to the bug)

[elasticmachine]

Pinging @elastic/security-solution (Team: SecuritySolution)

[elasticmachine]

💚 Build Succeeded

• Buildkite Build
• Commit: 44865f0

Metrics [docs]

Async chunks

Total size of all lazy-loaded chunks that will be downloaded as the user navigates the app

id	before	after	diff
securitySolution	10.3MB	10.3MB	+39.0B

[kibanamachine]

Friendly reminder: Looks like this PR hasn’t been backported yet.
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cc: @stephmilovic