CI: run Prettier over 2023 blog entries from now on

[chalin]

• Contributes to CI: check file formatting, including markdown #1063

• Changes ignore rules so that blog/2023 entries will be checked from now on for formatting issues.

  ⚠️ @svrnm @cartermp - after this PR is merged, ensure that any pending blog PRs are rebased before being merged.

• Disables the "singleQuote": true Prettier option because otherwise it reformats even code blocks like YAML. For an example, see below.

• Let's contributors know how to run tests

---

Example of why I disabled singleQuote

When singleQuote is enabled it changes YAML code blocks like the following, which we don't want IMHO:

$ git diff content/en/blog/2023/jmx-metric-insight/index.md 
diff --git a/content/en/blog/2023/jmx-metric-insight/index.md b/content/en/blog/2023/jmx-metric-insight/index.md
index abdfb27..02692cc 100644

--- a/content/en/blog/2023/jmx-metric-insight/index.md
+++ b/content/en/blog/2023/jmx-metric-insight/index.md
@@ -2,7 +2,7 @@
 title: Gaining JMX Metric Insights with the OpenTelemetry Java Agent
 linkTitle: JMX Metric Insight
 date: 2023-01-17
-author: "[Samudraneel Dasgupta](https://github.com/Samudraneel24) (Cisco)"
+author: '[Samudraneel Dasgupta](https://github.com/Samudraneel24) (Cisco)'
 ---
 
 [JMX](https://www.oracle.com/technical-resources/articles/javase/jmx.html) (Java
@@ -128,10 +128,10 @@ global:
   evaluation_interval: 10s
 
 scrape_configs:
-  - job_name: "my-kafka-broker"
+  - job_name: 'my-kafka-broker'
     scrape_interval: 5s
     static_configs:
-      - targets: ["host.docker.internal:9464"]
+      - targets: ['host.docker.internal:9464']

The scrape_configs changes are inside a code block.