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_auth_header.md

@@ -0,0 +1,65 @@
+# Validator Client API: Authorization Header
+
+## Overview
+
+The validator client HTTP server requires that all requests have the following
+HTTP header:
+
+- Name: `Authorization`
+- Value: `Bearer <api-token>`
+
+Where `<api-token>` is a string that can be obtained from the validator client
+host. Here is an example of the `Authorization` header:
+
+```text
+Authorization: Bearer hGut6B8uEujufDXSmZsT0thnxvdvKFBvh
+```
+
+## Obtaining the API token
+
+The API token is stored as a file in the `validators` directory. For most users
+this is `~/.lighthouse/{network}/validators/api-token.txt`, unless overridden using the
+`--http-token-path` CLI parameter. Here's an
+example using the `cat` command to print the token for mainnet to the terminal, but any
+text editor will suffice:
+
+```bash
+cat ~/.lighthouse/mainnet/validators/api-token.txt
+hGut6B8uEujufDXSmZsT0thnxvdvKFBvh
+```
+
+When starting the validator client it will output a log message containing the path
+to the file containing the api token.
+
+```text
+Sep 28 19:17:52.615 INFO HTTP API started                        api_token_file: "$HOME/holesky/validators/api-token.txt", listen_address: 127.0.0.1:5062
+```
+
+The _path_ to the API token may also be fetched from the HTTP API itself (this endpoint is the only
+one accessible without the token):
+
+```bash
+curl http://localhost:5062/lighthouse/auth
+```
+
+Response:
+
+```json
+{
+    "token_path": "/home/karlm/.lighthouse/holesky/validators/api-token.txt"
+}
+```
+
+## Example
+
+Here is an example `curl` command using the API token in the `Authorization` header:
+
+```bash
+curl localhost:5062/lighthouse/version -H "Authorization: Bearer hGut6B8uEujufDXSmZsT0thnxvdvKFBvh"
+```
+
+The server should respond with its version:
+
+```json
+{"data":{"version":"Lighthouse/v0.2.11-fc0654fbe+/x86_64-linux"}}
+```