Adopt updated camouflage-server & fix test_dfp_mlflow_model_writer

[dagardner-nv]

Description

• Adopt camouflage-server 0.15, previously we've been locked on v0.9 due to outstanding bugs introduced in versions 0.10 - 0.14.1 :
  • TypeError in v0.10.1 when validation is disabled testinggospels/camouflage#203
  • text/plain treated as json testinggospels/camouflage#223
  • Receiving html <br> tags instead of \n in response testinggospels/camouflage#227
  • File helper: Error: Can't set headers after they are sent. testinggospels/camouflage#229
• Includes unrelated fix to running CI locally
• Restrict mlflow to versions prior to 2.7

closes #967
Fixes #1192

By Submitting this PR I confirm:

• I am familiar with the Contributing Guidelines.
• When the PR is ready for review, new or existing tests cover these changes.
• When the PR is ready for review, the documentation is up to date with these changes.

[dagardner-nv]

/merge