add openapi spec for existing api

[w3irdrobot]

adds an openapi v3.1 document describing the current api. we can use this document to iterate on what a new version of the api might look like. there's alot of existing tooling that exist for this format that the community can utilize to make working with our apis easier.

the idea for this came from #667 (comment)

to view, docker can be used.

docker run -p 8080:8080 \
    -e SWAGGER_JSON=/workspace/swagger.json  \
    -v $PWD/main/http_server/openapi.yaml:/workspace/swagger.json \
    docker.swagger.io/swaggerapi/swagger-ui

open up localhost:8080 in a browser to view the docs using the swagger ui tool.

the contents of the file can also just be copy and pasted into the online editor as well.

in the future, we can consider options around hosting this, maybe making it available on the bitaxe itself?