docs: add more warnings for default secrets and docker-compose

[dpgaspar]

SUMMARY

Add more warnings on our default for docker-compose and stress out the importance of having a unique random SECRET_KEY

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]

One thing I was thinking about recently around ENVIRONMENT_TAG_CONFIG and SUPERSET_ENV is we could either force a very visible tag or refuse to start when use a bad combination of things (default SECRET_KEY and "SUPERSET_ENV=production").

Also was thinking that in-your-face, "things you should know" in dev would be useful, notices like "hey we noticed you're on python 3.9 - the supported version is now 3.10, you should upgrade"