Add notice fields to the metadata

[Mrpanda-Developer]

This feature adds a optional "install_message" before installing the package. In case of certain quirks with certain packages.

[BraveChicken1]

I think this change is a good idea, but I'm not sure if we should have two different fields in the package.toml file and targets.toml file. I think a message is mostly version specific, so having the field only in the targets.toml file is probably enough.

There are also two other things that would probably be nice to add:

• This field is now only for messages before an install, it would probably be nice to have two options: preinstall_notice and postinstall_notice.
• The notices probably need to be different on different platforms, so adding the field to both PackageVersionMeta and PackageTarget would give us the option to specify it globally for a version, or only for a specific target.

One final remark, these messages should probably be printed in the Installer::install_package function instead, next to the calls to execute_preinstall and execute_postinstall.

[Max13245]

I'm not sure if that many fields for comments is necessary, it might be. We could specify in the comment what it is meant for. Maybe it's nice to first only implement it more generally on the install. If we notice that we have a lot comments and need them to be more specific we can always add this functionality later. I do think it's good to already differentiate between targets though, because they are often very different.

[BraveChicken1]

My idea was to replace the two fields that are added in this PR, by a preinstall_notice and postinstall_notice field, to differentiate between the moment the message should be shown to the user.
For ca-certificates the postinstall_notice could be useful: it could show the user that the cert.pem file will be generated from the certificates that are installed in the OS.

[Max13245]

Ahh, so with pre and postinstall you just mean before and after the installation? I thought you meant you wanted to add something like this for all scripts (pre and postinstall being examples of script names), which seemed a bit overkill :)

[BraveChicken1]

Yes, exactly. I think a separation like that is useful, and the field name explains what it does clearly.

[Mrpanda-Developer]

Hey, those suggestions sound good to me, will implement them soon!

[Mrpanda-Developer]

I looked at your suggestions and implemented them, could you please give me some feedback on the changes wether they are good or not?

[BraveChicken1]

You forgot a few changes, see the suggestions below.

[Mrpanda-Developer]

whoops, yeah just saw. Should be fixed now.