Remove user identity validation from ReadFromEnv

[jkroepke]

external data sources depends on ReadFromEnv.

If and admin has enabled user identity, but didn't define a token_url, it would result into an error. It does matter if the data source supports user identity or not.

Bulit-in datasources doesn't have that issue, since they use ReadFromContext and doesn't have that restrictions.

grafana-azure-sdk-go/azsettings/settings.go

Lines 95 to 109 in c271284

	if v := cfg.Get(UserIdentityClientID); v != "" {
	settings.UserIdentityTokenEndpoint.ClientId = v
	}
	if v := cfg.Get(UserIdentityClientSecret); v != "" {
	settings.UserIdentityTokenEndpoint.ClientSecret = v
	}
	if v := cfg.Get(UserIdentityTokenURL); v != "" {
	settings.UserIdentityTokenEndpoint.TokenUrl = v
	}
	if v := cfg.Get(UserIdentityAssertion); v == "username" {
	settings.UserIdentityTokenEndpoint.UsernameAssertion = true
	}
	if v := cfg.Get(UserIdentityFallbackCredentialsEnabled); v == strconv.FormatBool(false) {
	settings.UserIdentityFallbackCredentialsEnabled = false
	}

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