This PR adds template substitution for the wrangler config files.

• <WORKER_NAME> is replaced with the worker name (from the project).
• <COMPATIBILITY_DATE> is replaced with the latest workerd date

This in in addition to how <TBD> is currently replaced by a context depend value (could be either the worker name or the compatibility date)

Notes:

• the new template substitution is applied before the legacy one to preserved backward compatibility.
• <WORKER_NAME> is needed to unblock Open Next (in a follow up PR)
• <COMPATIBILITY_DATE> is not currently used but will be used to make substitution clearer, see "Future work" below

For .json/.jsonc only the string values are considered.
For .toml it uses a simple string replace - which should be ok if we use uncommon key format.

Note / Future work:

We currently use this pattern for wrangler config / package.json:

{
	"name": "<TBD>",
	"main": "src/entry.py",
	"compatibility_date": "<TBD>",
	"compatibility_flags": ["python_workers"],
	"observability": {
		"enabled": true,
	},
}

IMO we should replace that with the mechanism of this PR for clarity, i.e.

{
	"name": "<WORKER_NAME>",
	"main": "src/entry.py",
	"compatibility_date": "<COMPATIBILITY_DATE>",
	"compatibility_flags": ["python_workers"],
	"observability": {
		"enabled": true,
	},
}

(We should keep the current logic for backward compatibility but update it and the templates)

• Tests
  • Tests included/updated
  • Tests not necessary because:
• Public documentation
  • Cloudflare docs PR(s):
  • Documentation not necessary because: internal
• Wrangler V3 Backport
  • Wrangler PR:
  • Not necessary because: c3