chore: retry failing tests in CI (#17681)

This PR introduces failing test retries in CI for e2e tests, Go tests
with the in-memory database, Go tests with Postgres, and the CLI tests.
Retries are not enabled for race tests.

The goal is to reduce how often flakes disrupt developers' workflows.

site/e2e/playwright.config.ts

@@ -10,12 +10,30 @@ import {
 } from "./constants";
 
 export const wsEndpoint = process.env.CODER_E2E_WS_ENDPOINT;
+export const retries = (() => {
+	if (process.env.CODER_E2E_TEST_RETRIES === undefined) {
+		return undefined;
+	}
+	const count = Number.parseInt(process.env.CODER_E2E_TEST_RETRIES, 10);
+	if (Number.isNaN(count)) {
+		throw new Error(
+			`CODER_E2E_TEST_RETRIES is not a number: ${process.env.CODER_E2E_TEST_RETRIES}`,
+		);
+	}
+	if (count < 0) {
+		throw new Error(
+			`CODER_E2E_TEST_RETRIES is less than 0: ${process.env.CODER_E2E_TEST_RETRIES}`,
+		);
+	}
+	return count;
+})();
 
 const localURL = (port: number, path: string): string => {
 	return `http://localhost:${port}${path}`;
 };
 
 export default defineConfig({
+	retries,
 	globalSetup: require.resolve("./setup/preflight"),
 	projects: [
 		{