Enable FF_TIMESTAMPS by default

Description

After a successful rollout of job log timestamps in gitlab.com, and having this feature enabled by default in GitLab runners we should be ready to enable this feature by default in new versions of runner.

• Enabled in gitlab.com instance runners, since Sept 2024: omnibus-gitlab!7929 (merged)
• Enabled in GitLab (rails), removal of feature flag as enabled in %17.2: gitlab!155695 (merged)
• Feedback issue (with no outstanding problems): gitlab#463391 (closed)

Technical Details

We should enable FF_TIMESTAMPS by default in an upcoming milestone (17.X), and prepare for removal of the feature flag in the next major version of runner (18.0).