Remove 1 year time bound limitation on vulnerability over time chart

What does this MR do and why?

This MR removes the 1-year time bound limitation on the vulnerability over time chart to address count inaccuracies across various charts and reports.

Context: The ES query on the vulnerabilities over time chart was time bounded for the last 1 year for performance reasons. However, this is causing count inaccuracies as reported in customer feedback (zendesk ticket).

Since the retention policy is not fully enabled and can take a longer time to roll out, we are removing this time bound limit.

Changes:

• Removed the overriden_created_after method from CountOverTimeFinder that was applying the 1-year limit
• Updated the execute method to use the actual created_after parameter from search_params instead of the overridden value
• Updated the spec to reflect that the passed arguments are used directly without override

ES query performance

Details are available in #581319 (comment 2899313830)

How to set up and validate locally

1. Ensure Elasticsearch is enabled and configured
2. Create vulnerabilities with various creation dates (including those older than 1 year)
3. Query the vulnerability over time chart
4. Verify that vulnerabilities older than 1 year are now included in the results

Local Verification

!213378 (comment 2901431617)

MR acceptance checklist

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Closes #581319 (closed)