chore(docs): updating alerts & reports documentation WEBDRIVER_BASEURL settings for docker compose

[fisjac]

SUMMARY

The existing documentation for enabling a headless webdriver do not work for the environment when using docker compose. Updating the docs to suggest using WEBDRIVER_BASEURL = "https://superset_app:8088" when running in docker compose.

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

TESTING INSTRUCTIONS

ADDITIONAL INFORMATION

• [ ] Has associated issue:
• [ ] Required feature flags:
• [ ] Changes UI
• [ ] Includes DB Migration (follow approval process in SIP-59)
  • [ ] Migration is atomic, supports rollback & is backwards-compatible
  • [ ] Confirm DB migration upgrade and downgrade tested
  • [ ] Runtime estimates and downtime expectations provided
• [ ] Introduces new feature or API
• [ ] Removes existing feature or API

[mistercrunch]

What about changing it here? -> https://github.com/apache/superset/blob/master/docker/pythonpath_dev/superset_config.py#L97-L99