fix(docker): optimize docker build by better utilizing build cache

[sebastianliebscher]

SUMMARY

The chown -R command causes the /app directory contents from previous COPY's to be copied up to the current layer. This results in additional redundant image size.
By using COPY --chown we can reduce the image size by ~130 MB.

Also

• remove duplicate COPY setup.py MANIFEST.in README.md /app/
• adjust indentation
• fix pip install option from --no-cache to --no-cache-dir

TESTING INSTRUCTIONS

docker build -t superset --no-cache .

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

[EugeneTorap]

Hi @villebro @dpgaspar! Would you like to review this interesting PR?

[villebro]

LGTM, great improvements and TIL about COPY --chown! Ping @dpgaspar @craig-rueda