Support for multiple trigger types in a single Spin application

[mikkelhegn]

This has been frequently mentioned in conversations, and also in issues (E.g., #1005), but I couldn't find an issue to track the request, so here it is.

A frequent Discord thread laid out a relevant scenario as well: https://discord.com/channels/926888690310053918/1149614859185569852

[vdice]

This is also being discussed in #1753

[carlokok]

I made a start (work in progress) on this:
main...carlokok:spin:feat/multiple-triggertypes

However before I continue, I would like to ask if this is an approach you'd all be oke with. (Note it's not done yet).

Essentially, trigger_type in up/app_source.rs returns a vector, and it spawns multiple trigger commands at once.

If this is oke, I'll continue working on it and do a PR when all works & tests are updated.

[itowlson]

@carlokok Thanks heaps for taking this on! The approach looks good to me, although there may be some nasties in the details (for example, spin up --help, the outbound HTTP to self, triggers using the same name for an option). Many of these will be fine to defer though.

cc @lann who has thought about this issue more deeply

[carlokok]

One thing I need to fix is that HTTP and REDIS use the old "trigger" field in the .lock file, instead of triggers. Once that's up I should have a working PR.