Expose entrypoint to py_image and py3_image rules

[mmikitka]

For issue #1247

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[mmikitka]

/gcbrun

[mmikitka]

/assign @smukherj1

[nlopezgi]

the preferred solution for this case is to do:

py_image(
  name= "py_base",
   ...
)

container_image(
  name="some_container",
  base = ":py_base",
  entrypoint="<new entrypoint>",
  ...
)

Let me know if that does not work for you for some reason.

[nlopezgi]

this is very similar to #498 (although the suggestion I made above is different than the one I made in #498, please do let me know if the suggestion works). Also see #309 for a longer discussion. Closing, but let me know if you want to reopen for some reason.