Add project files.

src/modules/Elsa.Sql/Contracts/ISqlClientFactory.cs

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+using Elsa.Sql.Client;
+
+namespace Elsa.Sql.Contracts;
+
+public interface ISqlClientFactory
+{
+    /// <summary>
+    /// Create an instance of the registered client.
+    /// </summary>
+    /// <param name="clientName">The name of the registered client to create. This can either be clientName used during registration or the default nameof(client) itself.</param>
+    /// <param name="connectionString">Connection string.</param>
+    /// <returns></returns>
+    public ISqlClient CreateClient(string clientName, string connectionString);
+}

src/modules/Elsa.Sql/Contracts/ISqlClientNamesProvider.cs

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+namespace Elsa.Sql.Contracts;
+
+public interface ISqlClientNamesProvider
+{
+    /// <summary>
+    /// Returns a dictionary of registered clients.
+    /// </summary>
+    /// <param name="cancellationToken">A token to monitor cancellation requests.</param>
+    /// <returns>A <see cref="Dictionary{TKey, TValue}"/> of registered client names their <see cref="Type"/>.</returns>
+    Task<IReadOnlyDictionary<string, Type>> GetRegisteredSqlClientNamesAsync(CancellationToken cancellationToken);
+}

src/modules/Elsa.Sql/Contracts/ISqlEvaluator.cs

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+using Elsa.Expressions.Models;
+using Elsa.Sql.Models;
+using JetBrains.Annotations;
+
+namespace Elsa.Sql.Contracts;
+
+/// <summary>
+/// Evaluates SQL expressions.
+/// </summary>
+[PublicAPI]
+public interface ISqlEvaluator
+{
+    /// <summary>
+    /// Evaluates a SQL expression.
+    /// </summary>
+    /// <param name="expression">The expression to evaluate.</param>
+    /// <param name="context">The context in which the expression is evaluated.</param>
+    /// <param name="options">A set of options.</param>
+    /// <param name="cancellationToken">An optional cancellation token.</param>
+    /// <returns>The <see cref="EvaluatedQuery"/> result.</returns>
+    Task<EvaluatedQuery> EvaluateAsync(
+        string expression,
+        ExpressionExecutionContext context,
+        ExpressionEvaluatorOptions options,
+        CancellationToken cancellationToken = default);
+}