Add --db-image argument to wasp deploy fly

[cprecioso]

• On top of Reorganize Fly docs #3186

Adds an optional --db-image argument to the wasp deploy fly {launch,setup,create-db} command, allowing the user to specify a custom Docker image for the database.

This is part of #3174. We're adding ask-the-documents to the repo, which needs a specific PostgreSQL extension. This way we can more easily test the app.

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[FranjoMindek]

Only thing, I would try to standardize the text between here and railway.
#3184

There will be changes, but e.g. start of the explanation could be the same:

By default standard version by {provider}.. if want different because of e.g. plugins ... specify yourself...

[Martinsos]

Makes sense, but I didn't dig into "is this correctly wired in all the places", I just look at the code changes and commented.
If you want somebody to check the first thing, probably best to have @infomiho take a look, or if you are confident, we can just go with it.

[Martinsos]

I would make it clear it is Docker image.
Also, why "with extensions"? Does it need to have extensions, why would that be so?

[Martinsos]

Suggested change

	## Using a Custom PostgreSQL Image
	## Using a Custom PostgreSQL Docker Image

I feel like we are not mentioning word Docker enough, we mostly just say image. That can be fine is context of Docker image is strongly established, but I don't think it is here, so I would at leats put it here in the title, to establish that context. ANd maybe I would even sprinkle Docker here and there below.

[Martinsos]

So this is me not knowing enough about how wasp deploy fly works, but what is the idea here, I need to keep repeating this argument for every command? How often do I need to repeat it, what does the workflow look like? How cumbersome / impractical is that -> it looks pretty impractical? What if they forget to pass it, what happens? If this is a problem, is there a better solution?

[Martinsos]

What about discoverability -> I am person building a Wasp app, and I used postgres extensions. Now I want to deploy to Fly. How likely am I to see this new piece of docs about custom docker image on Fly?

I guess I will look for it explicitly because I will know I need a custom Docker image, right? In that case I think we are fine.

But another thought. Wouldn't it be cool if Wasp knew you are using a custom docker image for development already, with extensions, and then when you are doing deployment, it prompted you also to provide a custom docker image? Or maybe even reused the same one you used for development? That might be interesting hm. Although I guess it can't be the same image because Fly has some config it expects from it. ALthough we could use that image locally, why not, based on Fly's image. Hm. So maybe optimal solution would be to have a place in Wasp where one can define databaes image, and then that same image is used by default both during development and also when deploying the database. This is also good because you normally want the development environment to be as similar to production environment as possible.

This certainly shouldn't be happening in this issue, but I thought it is a good moment to think about this.

[sodic]

Just like with Railway, There are plenty of reviewers here already so I won't take a detailed look unless you need me to.

I'll just say that this principle should also apply here:

• #3182 (review)
• #3183 (comment)