Add environment variables interpolation

[antonpetrov145]

Added the existing functionality to interpolate the environment set in compose.

Refers to 1384

[p12tic]

Tests are broken.

[antonpetrov145]

@p12tic seems the tests are passing now, what got me confused are these lines

os.environ.update({
    key: value  # type: ignore[misc]
    for key, value in dotenv_dict.items()
    if key.startswith("PODMAN_")  # type: ignore[misc]
})
self.environ = dotenv_dict  # type: ignore[assignment]
self.environ.update(dict(os.environ))

when we have the dotenv_dict from file we set self.environ to it and then update with whatever we have in os.environ which means that everything gets replaced back, so my mistake was that I tried to set the dotenv_dict with the interpolated values, then update the whole os.environ object before it gets assigned back to self.environ which seems that broke the test for env files

now I set the interpolation to be done directly on the self.environ object, tell me if the logic is not correct, but now all values get interpolated and set correctly

[p12tic]

Seems that the PR is still incomplete because 2 lines above we have self.environ = <...>.

Also, it would be great to have integration tests that show in a reproducible way what exactly didn't work before and is now fixed.

[p12tic]

Marking as "request changes" for myself

[antonpetrov145]

@p12tic you mean the lines above what I added right, I left those as they are because

self.environ = dotenv_dict  # here we are creating the self.environ obect

then here

self.environ.update(dict(os.environ))  # we are updating that with what we have in os.environ

and my change just interpolates the variables in the final object so there are no variables like $Abar

self.environ = rec_subs(dotenv_dict, dict(os.environ))

tell me if this logic is not correct, if I move the line above where we have the first assign, we will have the same result as now - variables are not interpolated because they are stored like that in os.environ