Fix SAST endpoint Issue

What does this MR do and why?

This MR fixes an Issue, that a renamed var coming from the BE was not renamed when it was parsed in template.

Renaming MR: !134968 (merged)

This merge request updates the endpoint_sast variable returned in diffs_tab_pane_data helper method to return a boolean instead of the path to the endpoint. The name of the variable was also changed to sast_report_available.

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. Enable sast_reports_in_inline_diff
2. Make sure your running an ultimate license or your GDK (how to)
3. Clone this repo: https://gitlab.com/jannik_lehmann/sast-inline-findings-example
4. Recreate this MR for SAST & CodeQuality findings: jannik_lehmann/cq-and-sast-test!5 (diffs)
5. Let the pipeline finish and the go checkout the diff page.
6. Reload page multiple times to see polling in action.

MR acceptance checklist

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• I have evaluated the MR acceptance checklist for this MR.