feat: return errors from resource.New (#59)

## Which problem is this PR solving?

When using detectors with mis-matched Schema URLs, resource.New will
return an error. Previously, this was dropped and consequently it looked
like configuration worked but many resource attributes would be missing
in the resulting telemetry.

With the recent addition of
#48, this error is
much easier to hit. For example, the detectors built into
opentelemetry-go
[import](https://github.com/open-telemetry/opentelemetry-go/blob/main/sdk/resource/builtin.go#L25)
semconv `v1.17.0` but this project [pulls
in](https://github.com/honeycombio/otel-config-go/blob/main/otelconfig/otelconfig.go#L21)
`v1.18.0`. This means that adding something like
`otelconfig.WithResourceOption(resource.WithHost())` results in a
mis-configured OTel and no error to warn you what happened.

This is all … very bad. This PR is really the bare minimum that needs to
be done here. That is, it at least causes a runtime error so that you
can tell what's going on — but it doesn't solve the problem that you
fundamentally cannot use this library with _any_ other library that
doesn't happen to use semconv `v1.18.0`. There are [a
number](open-telemetry/opentelemetry-go#2341)
of
[open](open-telemetry/opentelemetry-go#3769)
[issues](open-telemetry/opentelemetry-go-contrib#3657)
in OTel and adjacent repositories regarding this problem, which probably
warrant further investigation into a long-term sustainable solution.

## Short description of the changes

Return the `err` from `resource.New` up through the stack. Update tests
to expect this.

⚠️ I guess technically this could be considered a backwards incompatible
change, in that folks may have configurations that are "working" today
but will throw an error after this change. I put that in scare quotes
though because it's not _really_ working — it's just not throwing an
error. I feel like actually returning an appropriate error here and
letting folks know their configuration is likely not working as expected
is the right choice.

## How to verify that this has the expected result

There's a new test that specifically uses a detector with a different
schema URL.

Co-authored-by: Vera Reynolds <[email protected]>

otelconfig/otelconfig.go

@@ -331,7 +331,7 @@ type Config struct {
 	errorHandler                    otel.ErrorHandler
 }
 
-func newConfig(opts ...Option) *Config {
+func newConfig(opts ...Option) (*Config, error) {
 	c := &Config{
 		Headers:            map[string]string{},
 		TracesHeaders:      map[string]string{},
@@ -344,6 +344,8 @@ func newConfig(opts ...Option) *Config {
 	envError := envconfig.Process(context.Background(), c)
 	if envError != nil {
 		c.Logger.Fatalf("environment error: %v", envError)
+		// if our logger implementation doesn't os.Exit, we want to return here
+		return nil, fmt.Errorf("environment error: %w", envError)
 	}
 	// if exporter endpoint is not set using an env var, use the configured default
 	if c.ExporterEndpoint == "" {
@@ -366,8 +368,9 @@ func newConfig(opts ...Option) *Config {
 		l.logLevel = c.LogLevel
 	}
 
-	c.Resource = newResource(c)
-	return c
+	var err error
+	c.Resource, err = newResource(c)
+	return c, err
 }
 
 // OtelConfig is the object we're here for; it implements the initialization of Open Telemetry.
@@ -376,7 +379,7 @@ type OtelConfig struct {
 	shutdownFuncs []func() error
 }
 
-func newResource(c *Config) *resource.Resource {
+func newResource(c *Config) (*resource.Resource, error) {
 	r := resource.Environment()
 
 	hostnameSet := false
@@ -427,19 +430,14 @@ func newResource(c *Config) *resource.Resource {
 
 	options := append(baseOptions, c.ResourceOptions...)
 
-	r, err := resource.New(
+	// Note: There are new detectors we may wish to take advantage
+	// of, now available in the default SDK (e.g., WithProcess(),
+	// WithOSType(), ...).
+	return resource.New(
 		context.Background(),
 		options...,
 	)
 
-	if err != nil {
-		c.Logger.Debugf("error applying resource options: %s", err)
-	}
-
-	// Note: There are new detectors we may wish to take advantage
-	// of, now available in the default SDK (e.g., WithProcess(),
-	// WithOSType(), ...).
-	return r
 }
 
 type setupFunc func(*Config) (func() error, error)
@@ -616,7 +614,10 @@ func setupMetrics(c *Config) (func() error, error) {
 // ConfigureOpenTelemetry is a function that be called with zero or more options.
 // Options can be the basic ones above, or provided by individual vendors.
 func ConfigureOpenTelemetry(opts ...Option) (func(), error) {
-	c := newConfig(opts...)
+	c, err := newConfig(opts...)
+	if err != nil {
+		return nil, err
+	}
 
 	if c.LogLevel == "debug" {
 		c.Logger.Debugf("debug logging enabled")