Open WebUI provider

[deathbeam]

Provider for https://docs.openwebui.com/

docker run -d -p 3000:8080 --gpus=all -v ollama:/root/.ollama -v open-webui:/app/backend/data --name open-webui --restart always ghcr.io/open-webui/open-webui:ollama

require('CopilotChat.config').providers.openwebui = {
    prepare_input = require('CopilotChat.config.providers').copilot.prepare_input,
    prepare_output = require('CopilotChat.config.providers').copilot.prepare_output,

    get_headers = function()
        local api_key = assert(os.getenv('OPENWEBUI_API_KEY'), 'OPENWEBUI_API_KEY env not set')
        return {
            Authorization = 'Bearer ' .. api_key,
            ['Content-Type'] = 'application/json',
        }
    end,

    get_models = function(headers)
        local response, err = require('CopilotChat.utils').curl_get('http://localhost:3000/api/models', {
            headers = headers,
            json_response = true,
        })

        if err then
            error(err)
        end

        return vim.tbl_map(function(model)
            return {
                id = model.id,
                name = model.id,
            }
        end, response.body.data)
    end,

    get_url = function()
        return 'http://localhost:3000/api/chat/completions'
    end,
}