docs(a): add documentation for max price (#639)

* add documentation for maxPricePerUnit, ignoreMaxPriceIfNeeded and maxPricePerCapability

* refactor(ai): create seperate gateway maxPrice config section

This commit restructures the pull request so that the maxPrice
configuration for the gateway has its own section.

---------

Co-authored-by: Rick Staa <[email protected]>

ai/gateways/onchain.mdx

@@ -42,6 +42,63 @@ for more information. Here’s a summary of the key steps:
     - `-ethPassword=/root/.lpData/.eth_secret`: Sets the path to the Ethereum keystore password file.
     - `-ethOrchAddr=<MAIN_ORCH_ETH_ADDRESS>`: Sets the Ethereum address of the Mainnet Transcoding Network Gateway.
     - `-maxTotalEV=100000000000000`: Ensures the AI Gateway complies with the max ticket value limits in `go-livepeer`.
+    - `-maxPricePerUnit=<MAX PRICE in WEI or USD>`: This defaults to 0. Set to acceptable max price in wei (or USD, e.g. 0.02USD) willing to pay. Note: this can impact amount of Orchestrators available to process the work.
+    - `-ignoreMaxPriceIfNeeded=<true or false>`: This defaults to false. Set to true if want to process requests if no Orchestrators are under maxPricePerUnit or do not want to use a max price.
+    - `-maxPricePerCapability=/path/to/maxPrices.json`: This flag sets the max price per unit for one or many pipeline/models. Refer to the [Set Max Price Per Pipeline and Model](#set-max-price-per-pipeline-and-model-optional) section for more details.
 
   </Step>
 </Steps>
+
+## Set Max Price Per Pipeline and Model (Optional)
+
+To avoid overpaying for AI inference jobs, you can set a maximum price per unit
+for each pipeline and model. This feature is optional and can be configured
+using the `-maxPricePerCapability` flag. If a price is not set for a specific
+pipeline/model, the `-maxPricePerUnit` price will be used. The flag input should
+be a JSON file with the specified max prices. The example below demonstrates the
+following configurations:
+
+- Set the price for the `image-to-image` pipeline and model
+  `ByteDance/SDXL-Lightning` to 1,700,000 wei per unit (pixels).
+- Set the price for the `text-to-image` pipeline and model
+  `stabilityai/stable-diffusion-3-medium-diffusers` to 4,768,371 wei per unit
+  (pixels).
+- Set the price for the `upscale` pipeline for all models to 4,768,371 wei per
+  unit. The `pixels_per_unit` defaults to `1` if not specified.
+- Set the price for the `image-to-video` pipeline for all models to 3,390,842
+  wei per unit (pixels).
+- Set the price for the `audio-to-text` pipeline for all models to 12,882,811
+  wei per unit (milliseconds of audio).
+
+```json
+{
+  "capabilities-prices": [
+    {
+      "pipeline": "image-to-image",
+      "model_id": "ByteDance/SDXL-Lightning",
+      "price_per_unit": 1700000,
+      "pixels_per_unit": 1
+    },
+    {
+      "pipeline": "text-to-image",
+      "model_id": "stabilityai/stable-diffusion-3-medium-diffusers",
+      "price_per_unit": 4768371,
+      "pixels_per_unit": 1
+    },
+    {
+      "pipeline": "upscale",
+      "model_id": "default",
+      "price_per_unit": 4768371
+    },
+    {
+      "pipeline": "image-to-video",
+      "price_per_unit": 3390842,
+      "pixels_per_unit": 1
+    },
+    {
+      "pipeline": "audio-to-text",
+      "price_per_unit": 12882811,
+    }
+  ]
+}
+```