## Problem
The `src/proxy.rs` file is far too large
## Summary of changes
Creates 3 new files:
```
src/metrics.rs
src/proxy/retry.rs
src/proxy/connect_compute.rs
```
## Problem
Our serverless backend was a bit jumbled. As a comment indicated, we
were handling SQL-over-HTTP in our `websocket.rs` file.
I've extracted out the `sql_over_http` and `websocket` files from the
`http` module and put them into a new module called `serverless`.
## Summary of changes
```sh
mkdir proxy/src/serverless
mv proxy/src/http/{conn_pool,sql_over_http,websocket}.rs proxy/src/serverless/
mv proxy/src/http/server.rs proxy/src/http/health_server.rs
mv proxy/src/metrics proxy/src/usage_metrics.rs
```
I have also extracted the hyper server and handler from websocket.rs
into `serverless.rs`
## Problem
It took me a while to understand the purpose of all the tasks spawned in
the main functions.
## Summary of changes
Utilising the type system and less macros, plus much more comments,
document the shutdown procedure of each task in detail
In order to not to create NodePorts for each compute we can setup
services that accept connections on wildcard domains and then use
information from domain name to route connection to some internal
service. There are ready solutions for HTTPS and TLS connections
but postgresql protocol uses opportunistic TLS and we haven't found
any ready solutions.
This patch introduces `pg_sni_router` which routes connections to
`aaa--bbb--123.external.domain` to `aaa.bbb.123.internal.domain`.
In the long run we can avoid console -> compute psql communications,
but now this router seems to be the easier way forward.
