feat: document metrics, disable most libp2p metrics by default (#5457)

Author: David Himmelstrup

CHANGELOG.md

@@ -36,6 +36,8 @@
 ### Removed
 
 - [#5449](https://github.com/ChainSafe/forest/pull/5449) Remove unnecessary/duplicate metrics.
+- [#5457](https://github.com/ChainSafe/forest/pull/5457) Remove most prometheus
+  metrics starting with `libp2p_`.
 
 ### Fixed
 

docs/docs/users/reference/env_variables.md

@@ -31,6 +31,7 @@ process.
 | `FOREST_TEST_RNG_FIXED_SEED`                              | non-negative integer             | empty                                          | 0                                                             | Override RNG with a reproducible one seeded by the value. This should never be used out of test context for security. |
 | `RUST_LOG`                                                | string                           | empty                                          | `debug,forest_libp2p::service=info`                           | Allows for log level customization.                                                                                   |
 | `FOREST_IGNORE_DRAND`                                     | 1 or true                        | empty                                          | 1                                                             | Ignore Drand validation.                                                                                              |
+| `FOREST_LIBP2P_METRICS_ENABLED`                           | 1 or true                        | empty                                          | 1                                                             | Include `libp2p` metrics in Forest's Prometheus output.                                                               |
 | `FOREST_F3_SIDECAR_RPC_ENDPOINT`                          | string                           | 127.0.0.1:23456                                | `127.0.0.1:23456`                                             | An RPC endpoint of F3 sidecar.                                                                                        |
 | `FOREST_F3_SIDECAR_FFI_ENABLED`                           | 1 or true                        | hard-coded per chain                           | 1                                                             | Whether or not to start the F3 sidecar via FFI                                                                        |
 | `FOREST_F3_CONSENSUS_ENABLED`                             | 1 or true                        | hard-coded per chain                           | 1                                                             | Whether or not to apply the F3 consensus to the node                                                                  |