Selenium Grid: Trigger param enableManagedDownloads set as true by default

[VietND96]

• When enableManagedDownloads is true, it works for both cases it enabled (env var SE_NODE_ENABLE_MANAGED_DOWNLOADS=true is set) and it disabled.
• To avoid confusion for people who enabled this in Node but might miss this config in trigger param, so switch it to true by default.

Checklist

• When introducing a new scaler, I agree with the scaling governance policy
• I have verified that my change is according to the deprecations & breaking changes policy
• Tests have been added
• Changelog has been updated and is aligned with our changelog requirements
• A PR is opened to update our Helm chart (repo) (if applicable, ie. when deployment manifests are modified)
• A PR is opened to update the documentation on (repo) (if applicable)
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Fixes #

Relates to #

[JorTurFer]

/run-e2e selenium
Update: You can check the progress here