Some updates to Lighthouse book (#6995)

* #6447


  - Move some deprecated pages to a new section under `Archived`

- Remove fallback log in mev as the log will not be present after VC using `/eth/v3/validator/blocks` endpoint by default
- Add warning against using Btrfs file system (thank you @ChosunOne for the report)
- Add data shared by @mcdee  on tree states API queries time
- Rename partial withdrawals to validator sweep to differentiate it from the upcoming execution layer partial withdrawals
- Update NAT API response
- Update docs on IPv6

- Rename .md files to follow a standard prefix section name, e.g., installation_*.md, advanced_*.md
- Standardise .md files using underscore `_` instead of hyphen `-` to be consistent with other files naming conventions.

book/src/api_vc.md

@@ -0,0 +1,43 @@
+# Validator Client API
+
+Lighthouse implements a JSON HTTP API for the validator client which enables programmatic management
+of validators and keys.
+
+The API includes all of the endpoints from the [standard keymanager
+API](https://ethereum.github.io/keymanager-APIs/) that is implemented by other clients and remote
+signers. It also includes some Lighthouse-specific endpoints which are described in
+[Endpoints](./api_vc_endpoints.md).
+
+> Note: All requests to the HTTP server must supply an
+> [`Authorization`](./api_vc_auth_header.md) header.
+
+## Starting the server
+
+A Lighthouse validator client can be configured to expose a HTTP server by supplying the `--http` flag. The default listen address is `http://127.0.0.1:5062`.
+
+The following CLI flags control the HTTP server:
+
+- `--http`: enable the HTTP server (required even if the following flags are
+ provided).
+- `--http-address`: specify the listen address of the server. It is almost always unsafe to use a non-default HTTP listen address. Use this with caution. See the  **Security** section below for more information.
+- `--http-port`: specify the listen port of the server.
+- `--http-allow-origin`: specify the value of the `Access-Control-Allow-Origin`
+  header. The default is to not supply a header.
+
+## Security
+
+The validator client HTTP server is **not encrypted** (i.e., it is **not HTTPS**). For
+this reason, it will listen by default on `http://127.0.0.1`.
+
+It is unsafe to expose the validator client to the public Internet without
+additional transport layer security (e.g., HTTPS via nginx, SSH tunnels, etc.).
+
+For custom setups, such as certain Docker configurations, a custom HTTP listen address can be used by passing the `--http-address` and `--unencrypted-http-transport` flags. The `--unencrypted-http-transport` flag is a safety flag which is required to ensure the user is aware of the potential risks when using a non-default listen address.
+
+### CLI Example
+
+Start the validator client with the HTTP server listening on [http://localhost:5062](http://localhost:5062):
+
+```bash
+lighthouse vc --http
+```