Fix Model Selection tooltips not rendering in Vue 3

What does this MR do and why?

• Fix the "Apply to all" tooltip not rendering in Vue 3 on the instance-level and namespace-level Model Selection pages.
• Fix the warning tooltip not rendering in Vue 3 when no model is selected for a feature in the instance-level Model Selection page (offline mode)

Root cause: batch_update_button.vue and batch_settings_updater.vue used the GlTooltip component with :target="() => $refs.someRef". In Vue 3, $refs are not populated during the initial render when the tooltip component evaluates its target function, so the tooltip received a null target and rendered an empty container. Since there is a company wide effort to migrate to Vue 3 right now, this is important to fix.

Fix: Replace the GlTooltip component with the v-gl-tooltip directive, which is the Vue 3-compatible approach already used by sibling components in the same directory (available_models_row.vue, model_select_dropdown.vue, etc.).

Closes #624686 (closed)

References

• Issue: #624686 (closed)
• Related MR: !248438 (merged)
• Related discussion: !248438 (comment 3750436663)

Screenshots or screen recordings

SaaS (Vue3)

Before	After

Self-managed online (Vue3)

Before	After

Self-managed offline (Vue3)

Before	After

How to set up and validate locally

• Switch GDK to Vue 3:

  gdk config set vite.vue_version 3
  gdk reconfigure
  gdk restart

Validating instance-level model selection

1. Go to /admin/gitlab_duo/model_selection/features.
2. Hover over the Apply to all button — tooltip should now render with helper text.
3. Hover over the warning icon when no model is assigned (for offline mode only) — tooltip should now render with helper text.

Validating namespace-level model selection

2. Go to /groups/gitlab-duo/-/settings/gitlab_duo/model_selection (where gitlab-duo is the group ID)
3. Hover over the Apply to all button — tooltip should now render with helper text.

Validating no regressions in Vue2

• Repeat steps above with GDK in Vue 2

MR acceptance checklist

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