Add standard Overture issue template and field sync workflow

[ericgodwin]

Description

OvertureMaps/docs has no .github/ISSUE_TEMPLATE/ directory at all — every issue is filed blank. Bring the repo in line with the GitHub usage operating procedures by adding the standard Overture issue form and the org field sync workflow, using tf-data-platform as the reference implementation.

Add:

• .github/ISSUE_TEMPLATE/overture.yaml — the single Overture template. Adds new issues to the Overture project (OvertureMaps/84) and prompts for Type, Scope, and Skillset, plus a required Description textarea.
• .github/ISSUE_TEMPLATE/config.yml — blank_issues_enabled: false, so the template is always used.
• .github/workflows/sync-issue-type-and-scope.yml — runs OvertureMaps/workflows/.github/actions/sync-issue-fields@main on issues: opened to copy the form answers into the org-level fields.

Field values:

• Type: Task, Bug, Agenda — no Feature (dropped in OvertureMaps/tf-data-platform#4728).
• Scope: Addresses, Base, Buildings, Divisions, Places, Transportation, Multi-theme or Platform.
• Skillset: data analysis, data science, dev ops, engineering.

No option is pre-selected on any of the three dropdowns — the submitter picks a value.

Context

• OvertureMaps/tf-data-platform#4623 established the standard template layout across Overture-managed repos.
• OvertureMaps/tf-data-platform#4728 added the Skillset dropdown and removed Feature from Type.
• The operating procedures require all Overture-managed repos to offer the same templates, add every new issue to the Overture project, and capture Type / Scope / Skillset at creation time.
• Existing docs issue titles use bracketed prefixes ([BUG], [ENHANCEMENT]). Per the guidelines the template must not prepend a bracketed type to the title — the Type field carries that information.

Constraints

• Only one template is needed for this repo — the Overture template. There is no task force project scoped to docs, and no meeting agenda template.
• Skillset option strings must match the org field options exactly (lowercase) or the sync will 422.
• id: skillset must stay as-is to match the skillset-form-field default in the shared action.
• docs is a public repo, so the template is the first thing external contributors see — keep the prompt text approachable.
• The sync action is referenced at @main (matching tf-data-platform), which trips the unpinned-action lint; carry the same # zizmor: ignore[unpinned-uses] comment.

Acceptance criteria

• .github/ISSUE_TEMPLATE/overture.yaml exists, targets project OvertureMaps/84, and has type, scope, skillset, and description fields, all required
• All Type, Scope, and Skillset options listed above are present, with no default: on any dropdown
• Feature is not offered as a Type
• .github/ISSUE_TEMPLATE/config.yml sets blank_issues_enabled: false
• .github/workflows/sync-issue-type-and-scope.yml exists and matches the tf-data-platform version
• The template does not prepend a bracketed type to the issue title

Test plan

• Confirm both YAML files parse and the template renders in the "New issue" chooser with no schema errors.
• Confirm required-field validation blocks submission when a dropdown is left unselected.
• Open a test issue from the template, confirm it lands in the Overture project and that the sync workflow populates the org-level Type, Scope, and Skillset fields, then close it.
• Confirm the blank-issue option is gone from the chooser.

Initial design details and thoughts

Copy overture.yaml, config.yml, and sync-issue-type-and-scope.yml verbatim from OvertureMaps/tf-data-platform so the repos stay byte-identical and future updates can be applied uniformly. The only judgement call is whether the Description placeholder should be reworded for a docs audience; defaulting to leaving it identical.