Allow site configuration to not index tag pages

### Motivation

#### Why

Tag pages are thin/low quality, creating duplicated content.
This leads to search engines scoring the website lower, or indexing tag pages before the specific pages.

Google says [1]:

> Block crawling of duplicate content on your site, or unimportant resources (such as small, frequently used graphics such as icons or logos) that might overload your server with requests. Don't use robots.txt as a mechanism to prevent indexing; use the noindex tag or login requirements for that

I have solved this through wrapping/swizzling list pages, tag components and and custom `sitemap.ignorePatterns` rule in the config file, but it's a lot of workaround and a **best-practice** like this would be appreciated if it came as default.

#### Background

This has lead to me issues with all search engines for [privacylearn.com](https://privacylearn.com) to present open-source scripts pre-launch.

siteliner analysis:

Google indexing status:

Engines include Google, Yandex and Bing where thousands of my pages got de-indexed over time and tags pages took more priority than proper pages.

[1]: https://developers.google.com/search/docs/fundamentals/get-started#robots.txt

### API design

_No response_

### Have you tried building it?

_No response_

### Self-service