feat: support with_cmd for GenericImage

[tisonkun]

This closes #701.

@DDtKey I'm new to here so perhaps you can tell me some conveniences and best practices if I miss them :D

[netlify]

✅ Deploy Preview for testcontainers-rust ready!

Name	Link
🔨 Latest commit	d289269
🔍 Latest deploy log	https://app.netlify.com/sites/testcontainers-rust/deploys/669c52cd2c551c0008d95dc4
😎 Deploy Preview	https://deploy-preview-703--testcontainers-rust.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

---

To edit notification comments on pull requests, go to your Netlify site configuration.

[tisonkun]

Seems some logic conflicts. Let me try to debug locally.

[DDtKey]

I remembered why the cmd isn't exposed as part of the GenericImage.

It produces fully duplicative methods with ImageExt for no reason actually. Currently only essential options are provided as part of GenericImage api (which are not available within ImageExt)

Also, it would lead to unnecessary name collisions (not critical, but also - for no reason).

Let's say if we add cmd, why other options shouldn't be available? There is no benefit, but unnecessary confusion, actually

Moreover, the common way to go is usually implementation of custom Image (or use provided) rather than using generic one.

I apologize for this, but I have to reject the PR unless there is a strong reason for this.

Thank you 🙏

[tisonkun]

Sounds reasonable. Never mind :D