Update samples to Gramine v1.6

[daniel-weisse]

Gramine released v1.6 a while ago, but this wasn't picked up by renovate since they also changed the tag format used for the images.

Proposed changes

• Update samples to use Gramine v1.6
  • Run chmod on start.sh to fix potential issue when building container image
  • Use --insecure flag to check status of Coordinator before manifest is set
• Remove mention of exact Gramine version in sample Readmes, we test against the latest Gramine version in our CI anyways

Additional info

• Tested changes manually on Gramine v1.6
• New redis image needs to be build after this PR is merged

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