image-pull: add e2e execution time plot

[csegarragonz]

The idea is to compare the execution time of SC2 with different image-pulling configurations:

• Guest pull (regular) image-pull: add benchmark comparing image pull mechanisms #18
• Lazy guest pull (w/ nydus) image-pull: add benchmark comparing image pull mechanisms #18
• Host mount (w/ nydus) image-pull: add benchmark comparing image pull mechanisms #18
• Hybrid

Do for two different applications:

• helloworld-py image-pull: add benchmark comparing image pull mechanisms #18
• tflite inference (or something from a benchmark) image-pull: add benchmark comparing image pull mechanisms #18

For each mode and application, we will have:

• Unencrypted images image-pull: add benchmark comparing image pull mechanisms #18
• Encrypted images

Also, we need to remember to include in our measurements:

• A bar for function's runtime image-pull: add benchmark comparing image pull mechanisms #18

Known issues:

• TFlite does not work with host-mount (?)
• Hello World seems to trigger an error with host mount (seems to be in the transition between snapshotters)
• Host mount performance does not seem reasonable