[ENVOY] feat: Envoy to set Service ID header from subdomain

[commoddity]

This PR makes three main changes to PATH:

1. A new Envoy Proxy HTTP Filter to Extract the Service ID from request subdomain or header
2. Removes the concept of a service "alias" from PATH's code; instead all aliases are handled at the Envoy level.
3. Introduces a map in .allowed-services.lua to configure which services are allowed by a PATH instance.

Further details below.

1. Envoy Lua Filter
   Adds a new Lua HTTP filter to the Envoy YAML template to set the target-service-id header from the subdomain or the header (including resolving service aliases to authoritative service IDs - see point 2.).

"anvil.gateway.pokt.network" -> Header: "target-service-id: anvil"
"eth.gateway.pokt.network" -> Header: "target-service-id: F00C"

This allows us to continue supporting the legacy method of passing chain IDs to middleware via the subdomain.

eg.

curl http://localhost:3001/v1 \
    -X POST \
    -H "Content-Type: application/json" \
    -H "Endpoint-ID: 1a2b3c4d" \
    -H "Authorization: <API_KEY>" \
    -H "Target-Service-ID: anvil" \
    -d '{"jsonrpc": "2.0", "id": 1, "method": "eth_blockNumber" }'

and

curl http://anvil.localhost:3001/v1 \  
    -X POST \
    -H "Content-Type: application/json" \
    -H "Endpoint-ID: 1a2b3c4d" \
    -H "Authorization: <API_KEY>" \
    -d '{"jsonrpc": "2.0", "id": 1, "method": "eth_blockNumber" }'

both work when hitting Envoy (in the latter example, the new Envoy HTTP filter sets the Target-Service-ID header from anvil.localhost:3001).

2. Removal of service "alias" concept from PATH

tl;dr all service IDs forwarded to PATH from Envoy are 1. in the target-service-id header and 2. authoritative IDs, not aliases

All handling of service aliases requests is done at the Envoy Proxy level now, inside the Lua filter.

Allowed services for a PATH instance are now configured inside a new .allowed-services.lua file which is mounted into the Envoy Proxy container and read from inside the Lua filter.

If requests are made for a service that does not exist in this file they will be rejected.

Aliases are also configured here and the Lua filter ensures that requests made for aliases are forwarded to PATH with the correct authoritative service ID set as the target-service-id header.

NOTE: This PR also updates all header string consts in the Go code to be lowercase as the variable casing was causing issues with Envoy. Suggest that all header consts defined in the Go code be lower case going forward to avoid the potential for casing issues with Envoy. It also removes the deprecated x- prefix from header names.

[Olshansk]

LGTM!

Will approve after we merge the base and rebase this.

[Olshansk]

Just as a heads up - I'm skipping this in leu of time but will edit when going through the E2E flow again.

[commoddity]

Just as a heads up - I'm skipping this in leu of time but will edit when going through the E2E flow again.

SGTM but just FYI this file it not currently involved in the E2E at all.

I started playing around with how we could implement a FULL E2E suite utilizing Tilt to spin up the full stack including Envoy but it's non-trivial and will have to wait until the new year.

But just FYI I have been thinking about it and tentatively started prototyping.

[Olshansk]

@commoddity I updated the docs and made sure we can render mermaid diagrams, etc (it wasn't working before).

Let's merge it in!