Warn messages while using env prefix

We have people using environment variables to set config values. This is currently backward compatible but people are receiving messages because of the prefix:

  2024-11-10T16:07:38.447746Z  WARN indexer_config::config: Ignoring unknown configuration field: _host_and_port
    at config/src/config.rs:59

  2024-11-10T16:07:38.447805Z  WARN indexer_config::config: Ignoring unknown configuration field: _serve_escrow_subgraph
    at config/src/config.rs:59

  2024-11-10T16:07:38.447808Z  WARN indexer_config::config: Ignoring unknown configuration field: _serve_network_subgraph
    at config/src/config.rs:59

  2024-11-10T16:07:38.447810Z  WARN indexer_config::config: Ignoring unknown configuration field: _tap
    at config/src/config.rs:59

  2024-11-10T16:07:38.447811Z  WARN indexer_config::config: Ignoring unknown configuration field: _url_prefix
    at config/src/config.rs:59

This happens because we have in our config the following entries:

[service]
host_and_port = "0.0.0.0:7600"
url_prefix = "/"
serve_network_subgraph = false
serve_escrow_subgraph = false

And the way our prefix works, these environment variables are having some messages because of that:

INDEXER_SERVICE__SERVE_NETWORK_SUBGRAPH
INDEXER_SERVICE__SERVE_ESCROW_SUBGRAPH
INDEXER_SERVICE__HOST_AND_PORT
INDEXER_SERVICE__URL_PREFIX

Start at config/src/config.rs:59 and inspect how the INDEXER_SERVICE__ prefixed variables are handled for the listed configuration fields. Reproduce the warnings with the provided configuration and environment variable names; done means supported prefixed variables remain backward compatible without producing unknown-field warnings.