fix: Add xanchor config to line chart legends

[egcastro]

What this does

Fixed the legends positioning described here: https://linear.app/snyk/issue/FP-1101/visualization-meta-design-details

You have to pass the legend_x_anchor from the layer configuration to see this applied.

You can use this branch to test it: chore/exposure-line-chart

Notes for the reviewer

Instructions on how to run this locally, background context, what to review, best to review commit-by-commit?, questions…

Missed anything?

• [ ] Performance (customer with 200k users, customer with 1k orgs etc). Review the Performance documentation
• [ ] Security aspects considered? Unhappy paths?
• [ ] Have you accounted for accessibility?
• [ ] Commit messages and bodies explain what and why?

More information

• Slack thread
• [Jira ticket](https://snyksec.atlassian.net/browse/TEAM-0000)

  Screenshots / GIFs

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