go/proxyd: Add support for env vars in the config

gas-oracle: fix average block gas limit flag

The average block gas limit was converted to a uint64
from a float64, this commit updates the flag parsing
to parse the correct type.

integration-tests: Add actor testing framework, ACD actor tests

dtl: cleanly catch sigterm and sigint

feat: update whitelist task for multiple addresses

Added a polling cycle var to op-exporter

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Metadata:

- Fixes ENG-1662
- Fixes ENG-1664
- Fixes ENG-1663

Adds the actor testing framework and implements some basic actor tests. The tests are:

- An actor that makes repeated deposits
- An actor that makes repeated transfers

For information on how the framework works, see [integration-tests/actor-tests/README.md](integration-tests/actor-tests/README.md).

ci: standardize ci node version to 16

Certain config parameters can now be read from the environment if environment variables as provided as config values. The following parameters can be read from the environment:

- `backends.*.rpc_url`
- `backends.*.ws_url`
- `backends.*.password`
- `authentication.*`

Example backend config:

```toml
[backends]
[backends.from_env]
rpc_url = "$SECRET_RPC_URL"
ws_url = "$SECRET_WS_URL"
```

Example authentication config. Note the additional double quotes around the secret key:

```toml
[authentication]
"$SECRET_AUTH_KEY" = "auth_key_alias"
```

Env vars can be escaped with two backslashes (`\\`). We have to use two backslashes because it's also the escape character in TOML.

Env vars defined in the config but not defined in the actual environment will result in an error that prevents `proxyd` from starting.

Metadata:

- Fixes: ENG-1728

for reference these were moved to https://github.com/ethereum-optimism/optimistic-specs/tree/move-legacy-monorepo-specs

fix: don't round down average gas per epoch

The Github actions often run node.js. This commit
standardizes the usage of node.js to version 16,
the current LTS.

Develop -> Master Release PR

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fix: trigger node 16 releases

Upgrade the L1 hardhat node docker
image to use node version 16

changesets: don't track builder image

Tracking the builder image causes problems
in the CI. It started to be tracked when
there was a desire for faster builds. Publishing
a versioned builder image has resulted in
many CI publishing related bugs. This commit
removes tracking of the builder image.

Develop -> Master Release PR

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Develop -> Master PR

docker: update node version to 16

Develop -> Master Release PR

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