0.58.0-beta-sfx6

This release contains updates to Drupal instrumentation:

1. Drupal user IDs and roles appear at the root span under drupal.user.id and drupal.user.roles tags.
2. The executed Drupal view is available under drupal.view.execute span with the view name appearing under drupal.view tag.
3. New tag drupal.module under drupal.hook.* spans (or module_invoke_* for Drupal 7), showing which modules were executed during the hook.
4. Request headers can now be set to be captured with the SIGNALFX_CAPTURE_REQUEST_HEADERS environment variable. For example setting SIGNALFX_CAPTURE_REQUEST_HEADERS=User-Agent,X-My-Header will produce 2 tags under the root span: http.request.header.user_agent and http.request.header.x_my_header.
5. PHP environment variables can be set to be captured under the root span via SIGNALFX_CAPTURE_ENV_VARS env variable. Example: SIGNALFX_CAPTURE_ENV_VARS=MY_ENV_VAR will add php.env.my_env_var tag.
6. file_get_contents is now traced, but is disabled by default. Enabled via SIGNALFX_TRACE_FILE_GET_CONTENTS environment variable: SIGNALFX_TRACE_FILE_GET_CONTENTS=true.
7. json_decode, json_encode are traced, disabled by default. Enabled via SIGNALFX_TRACE_JSON environment variable: SIGNALFX_TRACE_JSON=true.
8. Drupal 8+: controller names are attached as drupal.controller for some of the drupal.event.* spans, e.g. drupal.event.kernel.controller or drupal.event.kernel.request.