Add tiny_relay variant files

- platformio.ini: Build configuration for tiny relay variant
- target.cpp/h: Hardware-specific implementation
- variant.h: Variant identification header

variants/tiny_relay/target.h

@@ -0,0 +1,59 @@
+#pragma once
+
+#define RADIOLIB_STATIC_ONLY 1
+#include <RadioLib.h>
+#include <helpers/ArduinoHelpers.h>
+#include <helpers/SensorManager.h>
+#include <helpers/radiolib/CustomSTM32WLxWrapper.h>
+#include <helpers/radiolib/RadioLibWrappers.h>
+#include <helpers/stm32/STM32Board.h>
+
+#define PIN_VBAT_READ A0
+#define ADC_MULTIPLIER (5 * 1.73 * 1000)
+
+class TinyRelayBoard : public STM32Board
+{
+  public:
+    void begin() override
+    {
+        STM32Board::begin();
+        pinMode(PA0, OUTPUT);
+        pinMode(PA1, OUTPUT);
+    }
+
+    const char *getManufacturerName() const override { return "Tiny Relay"; }
+
+    uint16_t getBattMilliVolts() override
+    {
+        analogReadResolution(12);
+        uint32_t raw = 0;
+        for (int i = 0; i < 8; i++) {
+            raw += analogRead(PIN_VBAT_READ);
+        }
+        return ((double)raw) * ADC_MULTIPLIER / 8 / 4096;
+    }
+
+    void setGpio(uint32_t values) override
+    {
+        // set led values
+        digitalWrite(PA0, values & 1);
+        digitalWrite(PA1, (values & 2) >> 1);
+    }
+
+    uint32_t getGpio() override
+    {
+        // get led value
+        return (digitalRead(PA1) << 1) | digitalRead(PA0);
+    }
+};
+
+extern TinyRelayBoard board;
+extern WRAPPER_CLASS radio_driver;
+extern VolatileRTCClock rtc_clock;
+extern SensorManager sensors;
+
+bool radio_init();
+uint32_t radio_get_rng_seed();
+void radio_set_params(float freq, float bw, uint8_t sf, uint8_t cr);
+void radio_set_tx_power(uint8_t dbm);
+mesh::LocalIdentity radio_new_identity();