Rename DAST CI/CD variables for the next major DAST release

What does this MR do?

Updates browser-based DAST documentation to use renamed CI/CD variables. The old name is no longer referenced, this can be found using an older version of the docs.

DAST 4 (proxy-based DAST, browser-based DAST) has been retrofitted to add aliases for the new variable names.

DAST 5 (browser-based DAST) understands both new and old variable names.

Related issues

Rename CI/CD variables in proxy-based DAST (#441803 - closed)

Outcome of review of variable names can be found at #431485 (comment 1719674903).

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