docs(adr): setting up adr, start to write 00001-plugin

[kwonoj]

Description:
One of the biggest challenge I had to deal with large codebase was finding out historical context for some behavior, in short why we do this from beginning? And sometimes, I made changes without knowing those context then find out changed attempt was already tried and not chosen for various reasons.

For those reason I came to believe maintaining some decision records, history even if it's some short form of text can be meaningful. Among those I am in favor of https://adr.github.io/ and would like to propose we'd do the similar thing.

As a first step, this PR attempts to create initial template - mostly blind copy-paste from https://github.com/mozilla/uniffi-rs/tree/main/docs/adr and trying to fill some gaps for the plugin features we are changing now. I don't have full context for all the stories of plugin as well, so I may ask @kdy1 to fill some gaps especially prior decisions we made & why we don't do it.

Related issue (if exists):

• [Meta] Plugin system for 2.0 #2635

[kwonoj]

@kdy1 please feel free to add commits or modify for the blank part of plugin docs.

[martindisch]

Thank you! I have been wondering what the deciding factors were between wasmtime and wasmer, so this ADR was perfect.