Fix diagnostic messages on update environment

[seanyeh]

Fixes #370

When updating an env with an invalid definition, UpdateEnvironmentWithRevision should return no error but with diagnostics

Testing

Because of this issue, we previously wouldn't reach here (which requires non-error but with diagnostics), but with this change, now we can, because UpdateEnvironmentWithRevision will now return no error but with diagnostics on invalid definitions

When updating an env with an invalid definition:

Before:

❯ go run ./cmd/esc env edit test3/abc/ghi
Error: updating environment definition: [0]
Diags: yaml: line 2: mapping values are not allowed in this context

exit status 1

Now:

❯ go run ./cmd/esc env edit test3/abc/ghi
Error: yaml: line 2: mapping values are not allowed in this context

Press ENTER to continue editing or ^D to exit

[seanyeh]

This is because on certain 4xx errors, the pulumi service returns an object without {..., "code": 4xx}

[IaroslavTitov]

Hmm, should we fix this in PS? Sounds like it's not following a required API contract?

[seanyeh]

I initially considered this but I think it's a much bigger lift - we follow this "pattern" in many routes where certain errors will return code and message by default, but otherwise not.

I think perhaps a better fix is to check the http response status code instead. @pgavlin I notice that we don't return the http response on 4xx/5xx errors, is this intentional?

[IaroslavTitov]

Hmm, should we fix this in PS? Sounds like it's not following a required API contract?