Migrate website blog to use supported plugin. (#14828)

I followed
https://squidfunk.github.io/mkdocs-material/setup/setting-up-a-blog/ to
migrate our existing blog posts to use the new blog plugin provided by
mkdocs-material. We've considered removing these old posts / the blog
entirely, but I still like hosting the content and think we should write
new posts at some point.

* Current blog: https://openxla.github.io/iree/community/blog/

![image](https://github.com/openxla/iree/assets/4010439/49093a62-f628-4a31-aadf-ce6b628a852c)

* New blog preview: https://scotttodd.github.io/iree/community/blog/

![image](https://github.com/openxla/iree/assets/4010439/27d89753-fcbd-49e2-a7f6-79cf367fbfba)

The plugin shows author info, preview excerpts, estimated read times,
etc. :


![image](https://github.com/openxla/iree/assets/4010439/f366ff24-4277-406c-8441-a2cd27cd15d8)


---

Also add a tags page and bump mkdocs-material version.
diff --git a/docs/website/mkdocs.yml b/docs/website/mkdocs.yml
index 1b6a147..20576e4 100644
--- a/docs/website/mkdocs.yml
+++ b/docs/website/mkdocs.yml
@@ -167,16 +167,21 @@
       - "community/index.md"
       - "Blog":
           - "community/blog/index.md"
-          - CUDA backend: "community/blog/2021-10-15-cuda-backend.md"
-          - Work in progress on Matrix Multiplication on CPU: "community/blog/2021-10-13-mmt4d.md"
-          - TFLite Support via TOSA: "community/blog/2021-07-19-tflite-tosa.md"
-
+      - "community/tags.md"
 plugins:
+  # https://squidfunk.github.io/mkdocs-material/setup/setting-up-a-blog/
+  - blog:
+      blog_dir: "community/blog"
+      blog_toc: true
+      post_url_date_format: yyyy-MM-dd
+      post_url_format: "{date}-{slug}"
+
   # https://squidfunk.github.io/mkdocs-material/setup/setting-up-site-search/
   - search
 
   # https://squidfunk.github.io/mkdocs-material/setup/setting-up-tags/
-  - tags
+  - tags:
+      tags_file: community/tags.md
 
   # https://github.com/mkdocs/mkdocs-redirects
   - redirects:
@@ -204,6 +209,9 @@
 
         # "blog/" moved under "community/"
         "blog/index.md": "community/blog/index.md"
-        "blog/2021-07-19-tflite-tosa.md": "community/blog/2021-07-19-tflite-tosa.md"
-        "blog/2021-10-13-mmt4d.md": "community/blog/2021-10-13-mmt4d.md"
-        "blog/2021-10-15-cuda-backend.md": "community/blog/2021-10-15-cuda-backend.md"
+        "blog/2021-07-19-tflite-tosa.md": "community/blog/posts/tflite-tosa.md"
+        "blog/2021-10-13-mmt4d.md": "community/blog/posts/mmt4d.md"
+        "blog/2021-10-15-cuda-backend.md": "community/blog/posts/cuda-backend.md"
+        # Some blog post names/paths changed when setting up the blog plugin
+        "community/blog/2021-07-19-tflite-tosa.md": "community/blog/posts/tflite-tosa.md"
+        "community/blog/2021-10-13-mmt4d.md": "community/blog/posts/mmt4d.md"