alloy(role): add documentation

- add README
- add argument_specs
- removed tags

roles/alloy/README.md

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+# `Grafana Alloy` role
+
+Installs and configures [Grafana Alloy](https://grafana.com/docs/alloy/latest/) on Debian-based systems.
+Optionally deploys a [Blackbox exporter](https://github.com/prometheus/blackbox_exporter) config and a [UniFi Poller](https://unpoller.com/).
+
+## Supported Distributions
+
+Should work on Debian-based distributions.
+
+## Required Arguments
+
+- `alloy_config_default`: The default Alloy configuration. Recomanded for configuration that hosts of a groupe share.
+
+## Optional Arguments
+
+- `alloy_config_additional`: Additional Alloy configuration appended to the default config. Recomanded for per host configuration
+- `alloy_cap_net_bind_service`: Grant Alloy the `CAP_NET_BIND_SERVICE` capability, allowing it to bind to privileged ports (<1024).
+
+### Blackbox Exporter 
+- `alloy_blackbox_exporter_config_default`: Default blackbox exporter configuration.
+- `alloy_blackbox_exporter_config_additional`: Additional blackbox exporter configuration appended to the default blackbox exporter config.
+
+### UniFi Poller
+
+- `alloy_unpoller_enabled`: Enable the UniFi Poller container to scrape UniFi metrics.
+- `alloy_unpoller_unifi_user`: Username for the UniFi controller used by unpoller, defaults to `unpoller`.
+- `alloy_unpoller_unifi_password`: Password for the UniFi controller. Required when `alloy_unpoller_enabled` is `true`.
+- `alloy_unpoller_unifi_url`: URL of the UniFi controller. Required when `alloy_unpoller_enabled` is `true`.