Allow running wrangler dev without an account_id

[jyn514]

Previously, running it with no account_id and no config in ~/.wrangler would give an error:

Error: config path does not exist /home/jnelson/.wrangler/config/default.toml. Try running `wrangler login` or `wrangler config`

This is not technically a regression from loading account_id lazily, because in wrangler 1.17 it would just error earlier that account_id was required:

🕵️  You can find your account_id in the right sidebar of your account's Workers page
Error: field `account_id` is required to deploy to workers.dev

However, it seems odd that you'd have to have an account to run an unauthenticated preview.
This changes wrangler to only require an account_id or config file if you're actually deploying your site.

Fixes #1525

[jyn514]

So, I'm hitting more test failures ... the current ones are

thread 'settings::toml::tests::deployments::it_gets_deployments_with_route_and_workers_dev_true' panicked at 'assertion failed: manifest.get_deployments(environment).is_err()', src/settings/toml/tests/deployments.rs:508:5

thread 'settings::toml::tests::deployments::it_gets_deployments_with_routes_and_workers_dev_true' panicked at 'assertion failed: manifest.get_deployments(environment).is_err()', src/settings/toml/tests/deployments.rs:523:5

---- settings::toml::tests::deployments::it_errors_on_get_deployments_missing_account_id stdout ----
thread 'settings::toml::tests::deployments::it_errors_on_get_deployments_missing_account_id' panicked at 'assertion failed: manifest.get_deployments(environment).is_err()', src/settings/toml/tests/deployments.rs:99:5

I think this is because they expect get_deployments to fail eagerly, but now this only fails in deploy().

[jyn514]

@Electroid this is ready for review.

[jyn514]

@caass mentioned wanting to test this with Durable Objects and KV namespaces, but I'm not sure how to do that ... happy to do so if someone can write up instructions. I tried wrangler generate durable-objects https://github.com/cloudflare/durable-objects-template, but wrangler dev gives errors even without my changes:

Error: HTTP status client error (400 Bad Request) for url (https://api.cloudflare.com/client/v4/accounts/e1706d218241c1230155b4f91b3218af/workers/scripts/durable-objects/edge-preview)

[jspspike]

Tested locally and seems to be working as intended, other than that one commented out tests it looks good to me