chore: make package template a proper Yarn workspace

[Mrtenz]

Explanation

The scripts/create-package/package-template directory was not previously listed as a Yarn workspace, which meant Yarn constraints were not checked against it. This made it easy for the template to drift out of alignment with the monorepo's other packages over time.

This PR adds the template to the workspaces list and gives it a real package name (@metamask/package-template) so that constraints can run against it. Fields that vary per package (description, directory name) remain as placeholders. Constraints are relaxed in two places where the template legitimately differs from real packages: the homepage uses a placeholder directory name, and the code owner check is skipped.

References

N/A

Checklist

• I've updated the test suite for new or updated code as appropriate
• I've updated documentation (JSDoc, Markdown, etc.) for new or updated code as appropriate
• I've communicated my changes to consumers by updating changelogs for packages I've changed
• I've introduced breaking changes in this PR and have prepared draft pull requests for clients and consumer packages to resolve them

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Note

Low Risk
Scaffolding and monorepo tooling changes only; no runtime product behavior.

Overview
Turns the new-package scaffold into a real workspace at packages/package-template named @metamask/package-template (marked private) so Yarn constraints keep it aligned with other packages, with targeted relaxations for placeholder homepage and skipped CODEOWNERS checks.

create-package now copies from that workspace path instead of scripts/create-package/package-template, skips build/test artifacts (dist/, coverage/, *.tsbuildinfo), and strips private from generated package.json files. Placeholder replacement uses the scoped template name in template files; root tsconfig references, teams.json, and the lockfile register the workspace.

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[mcmire]

We might want to move create-package itself into a workspace, but this is good on its own.

One question, but otherwise looks good.

[mcmire]

What do you think about putting this const at the top of the file along with the others?

[Mrtenz]

Makes sense, done!

[mcmire]

I tested out the create-package utility and yarn lint passes (aside from the requirement to assign a codeowner to the package). Looks good.