Generate compatibility_date in wrangler init and warn if it's missing

[kentonv]

We'd like everyone to specify a compatibility_date in their wrangler.toml going forward. This change both adds the date automatically to newly-generated wrangler.toml files, and warns when parsing old ones that are missing it.

See also the documentation change: cloudflare/cloudflare-docs#2289

[WalshyDev]

Ah great! I noticed this a few days ago and had it on my todo to report

I also notice the init does double quotes for the filled out values and single for the empty ones. Not sure if this is an issue, just an odd inconsistency

[jyn514]

Code looks fine, but @Electroid or @kabirsikand might want to take a look at the wording.

[jyn514]

I tested this locally - the warning looks like

⚠️  Your configuration file is missing compatibility_date, so a distant past date is assumed. To get the latest possibly-breaking bug fixes, add this line to your wrangler.toml:

    compatibility_date = "2021-09-14"

⚠️  For more information about compatibility dates, see: https://developers.cloudflare.com/workers/platform/compatibility-dates

and is shown whenever you run wrangler (I think being annoying is intentional).

[Electroid]

Wording is good with me. ✅