refactor(iroh-net): More renaming of endpoint to direct address (#2515)

## Description

The name "endpoint" is overloaded and we decided a while ago to not
use it for things other than `iroh_net::Endpoint`.  This further
renames more places that were called endpoint with the new name we
already introduced for them: direct address.  The direct address
naming is already used consistently on public APIs, this is only for
internal consistency.

## Breaking Changes

metric changed: `magicsock::metrics::Metrics::update_endpoints` ->
`Metrics::update_direct_addrs`.

## Notes & open questions

<!-- Any notes, remarks or open questions you have to make about the PR.
-->

## Change checklist

- [x] Self-review.
- [x] Documentation updates following the [style
guide](https://rust-lang.github.io/rfcs/1574-more-api-documentation-conventions.html#appendix-a-full-conventions-text),
if relevant.
- [x] Tests if relevant.
- [x] All breaking changes documented.

---------

Co-authored-by: Divma <26765164+divagant-martian@users.noreply.github.com>
Co-authored-by: Philipp Krüger <philipp.krueger1@gmail.com>

iroh-net/src/bin/iroh-relay.rs

@@ -106,7 +106,7 @@ struct Config {
     ///
     /// Defaults to `[::]:80`.
     ///
-    /// When running with `--dev` defaults to [::]:3340`.  If specified overrides these
+    /// When running with `--dev` defaults to `[::]:3340`.  If specified overrides these
     /// defaults.
     ///
     /// The Relay server always starts an HTTP server, this specifies the socket this will