Support customization of text in connection forms from connectors or other packages

[altvod]

Instead of creating Translatable instances with a fixed i18n domain from within the form, we need to implement some kind of factory that would be accessible via SR and would create translatables with a custom domain given a translation key.
Let's call it TextProvider. It would look something like this:

from dl_i18n.localizer_base import Translatable

class TextProvider:
    def get_translatable(self, text_key: str, default_i18n_domain: str) -> Translatable:
        ...

This TextProvider instance can be supplied to form factory instances so that they can implement a method like this:

SomeFormFactory:
    text_provider: TextProvider
    default_i18n_domain: str

    def get_translatable(self, text_key: str) -> Translatable:
        return self.text_provider.get_translatable(text_key, default_i18n_domain=self.default_i18n_domain)

Packages provide custom texts in their own i18n domains, and a list of these custom domains should be provided via settings to the TextProvider instance.

Internal issue: BI-4909

[altvod]

Exceptions also make use of the translatable texts, so it would be logical to also extend this interface to wherever the main exception-generating places are (e.g. USM, executors/adapters).