Standardization Request: use one of `generic`/`da-service` commitment type everywhere

Right now both of these names are used interchangeably, both in the spec

and in the code.

This leads to [redundant variables](https://github.com/ethereum-optimism/optimism/blob/5a1a18d0ceedc40aad99baf4359e06f09fc7b718/bedrock-devnet/devnet/__init__.py#L278) that literally have the same function:
```
if GENERIC_ALTDA:
docker_env['ALTDA_GENERIC_DA'] = 'true'
docker_env['ALTDA_SERVICE'] = 'true'
else:
docker_env['ALTDA_GENERIC_DA'] = 'false'
docker_env['ALTDA_SERVICE'] = 'false'
```
Both ALTDA_GENERIC_DA and ALTDA_SERVICE are used for the exact same purpose, but in different services (op-batcher/node use da-service, whereas da-server uses generic).

Would be preferable to use a single variable, as well as flag naming convention everywhere. I like `generic` better, but open to either. I can make a PR to refactor this if needed.

Start with bedrock-devnet/devnet/__init__.py around the GENERIC_ALTDA environment setup, then compare the da-service naming in op-batcher/node with the generic naming in da-server and the spec. The work is done when one agreed commitment-type and flag naming convention is used consistently without redundant variables across the referenced services.

Written by the indexing model from the issue text.