Add support for custom PyPI repository configuration

- Add pypi-url, pypi-username, and pypi-password inputs to action.yml
- Implement configurePipRepository() function in utils.ts to create pip.conf/pip.ini
- Integrate pip configuration into setup-python.ts workflow
- Add comprehensive unit tests for pip configuration functionality
- Update README.md with usage examples and documentation
- Automatically mask credentials in logs for security

Fixes #814

src/setup-python.ts

@@ -11,7 +11,8 @@ import {
   logWarning,
   IS_MAC,
   getVersionInputFromFile,
-  getVersionsInputFromPlainFile
+  getVersionsInputFromPlainFile,
+  configurePipRepository
 } from './utils';
 import {exec} from '@actions/exec';
 
@@ -159,6 +160,12 @@ async function run() {
       if (cache && isCacheFeatureAvailable()) {
         await cacheDependencies(cache, pythonVersion);
       }
+      const pypiUrl = core.getInput('pypi-url');
+      if (pypiUrl) {
+        const pypiUsername = core.getInput('pypi-username');
+        const pypiPassword = core.getInput('pypi-password');
+        await configurePipRepository(pypiUrl, pypiUsername, pypiPassword);
+      }
       const pipInstall = core.getInput('pip-install');
       if (pipInstall) {
         await installPipPackages(pipInstall);