feat: support most configurations with Declarative Config (#6694)

* Sync declarative config and env var support; add tests

* Move runtime specific evaluations to defaults (e.g. remote config, crashtracking, etc)

* Handle cloudPayloadTagging and installSignature

Author: mtoffl01

packages/dd-trace/src/config-helper.js

@@ -80,6 +80,7 @@ module.exports = {
    * @returns {string|undefined}
    * @throws {Error} if the configuration is not supported
    */
+  // This method, and callers of this method, need to be updated to check for declarative config sources as well.
   getEnvironmentVariable (name) {
     if ((name.startsWith('DD_') || name.startsWith('OTEL_') || aliasToCanonical[name]) &&
         !supportedConfigurations[name]) {