There is no integration into the web UI for AdGuard Home. This PR adds
* A Lua script for rpcd to interface with the AGH REST API
* ACL controls allowing JS code to call rpcd, uci, logread
* Menu entries to put AdGuard Home under Services
* Three UIs - status, logs, config

The Lua script supports three API calls:
* get_status - maps to /control/status in the AGH REST API
* get_statistics - maps to /control/stats in the AGH REST API
* get_config - converts /etc/adguardhome.yaml to JSON

Authentication details must be provided by the user, as the password in the YAML file is encrypted. This results in the AGH password being stored cleartext in /etc/config/adguardhome.

The Lua script will log if it encounters an error, in an effort to make it easier to debug. These logs are visible in the Logs UI of the application.

I could not find any unit testing for things like the UI or the Lua code, so the only testing done was by hand.

The credentials were removed from the config, and both the ubus call and the web UI render the failure to acquire the credentials.

Incorrect credentials were supplied, and the UI was verified as showing a RPC error message.

ACLs were checked by removing luci-compat.json (which wildcard allows saving/reading), and ensuring that the UI could read and save the config.

Package was built and tested with
```
 make package/luci-app-adguardhome/compile  -j20
 scp bin/packages/i386_pentium4/cricalixluci/luci-app-adguardhome_unknown_all.ipk root@192.168.0.1:
 ssh root@192.168.0.1
 opkg remove luci-app-adguardhome && opkg install luci-app-adguardhome_unknown_all.ipk && rm luci-app-adguardhome_unknown_all.ipk
```
and then browsing the UI to make sure the deployment was clean and behaved as expected.

Signed-off-by: Duncan Hill <openwrt-dev@cricalix.net>

…t on 23.05, format code