Restrict regions due to AppInsights error

## Purpose This pull request updates the `location` parameter in the `infra/main.bicep` file to restrict allowed deployment regions and add relevant metadata. The main change ensures that deployments can only be performed in regions supported by `microsoft.insights/components`. Resource region restrictions: * Added an `@allowed` decorator to the `location` parameter, listing all supported Azure regions for `microsoft.insights/components`. This prevents deployments in unsupported regions. * Added an `@metadata` decorator to the `location` parameter to specify its type as 'location' for azd. ## Does this introduce a breaking change? When developers merge from main and run the server, azd up, or azd deploy, will this produce an error? If you're not sure, try it out on an old environment. ``` [ ] Yes [X] No ``` ## Type of change ``` [X] Bugfix [ ] Feature [ ] Code style update (formatting, local variables) [ ] Refactoring (no functional changes, no api changes) [ ] Documentation content changes [ ] Other... Please describe: ``` ## Code quality checklist See [CONTRIBUTING.md](https://github.com/Azure-Samples/rag-postgres-openai-python/blob/main/CONTRIBUTING.md#submit-pr) for more details. N/A