Initialization script customization

[wcrbrm]

Motivation:

The intention behind this PR is to have full control over the script that initialized application and use trunk in more cases.
While in current version initialization templates are hardcoded, initialization may differ for other frameworks
and require more flexibility for debugging see Sauron SSR as example.

Changes:

• Added the optional pattern_script field to the Trunk.toml for overloading the template of initialization script.
• Added the optional pattern_preload field to the Trunk.toml for overloading the template of WASM preloading.
• Added the optional pattern_params field to the Trunk.toml for extending pattern_script and pattern_preload with additional values, even including external files.
• Parameters can be set up only in Trunk.toml and not from environment/CLI because they are typically multiline.

Backward compatibility is kept

Checklist

• Updated CHANGELOG.md describing pertinent changes.
• Updated README.md with pertinent info (may not always apply).
• Squash down commits to one or two logical commits which clearly describe the work you've done. If you don't, then Dodd will :).

[thedodd]

@wcrbrm hello there. Thanks for opening this PR. I can definitely see how there is value in being able to customize the JS init script used to load the WASM app. I'll circle back and give this a more in-depth review after v0.13 is released.

[thedodd]

@wcrbrm thanks for opening this PR! I apologize for how it has taken me to get around to reviewing this.

High-level, I like the approach. Seems quite flexible. Long-term, I think we should create a plugin which allows for full visibility of the manifest and all other outputs of the system. However, the plugin system is not ready yet, so this is quite good.

I have a few comments below about subtle changes which I think would be good. Let me know what you think.

• Before we merge, we need to add documentation on this feature, and the place to do that is the site folder. I would say that this should be added to the assets page.

[wcrbrm]

Thanks for detailed review and putting proper wording in docs!
Branch in its current state was checked and it works for the cases I have

Do you want me to modify site/content/assets.md page to describe it or you will do it?
I actually think these parameters refer to site/content/configuration.md, as they are not actually referring to assets, and available only in configuration file Trunk.toml

[thedodd]

@wcrbrm no worries. I'll update the site. Thank you!

[thedodd]

Awesome! Merging.

[thedodd]

I'm going to make a small tweak to this once I merge.