[MKC-1191] Bluetooth® Low Energy Learn Article

[Hannes7eicher]

What This PR Changes

This PR adds a Bluetooth® Low Energy Learn Article.

Contribution Guidelines

• I confirm that I have read the contribution guidelines and comply with them.

[gatsby-cloud]

✅ docs-content deploy preview ready

• Deploy preview
• Build logs · 2m build time

[jhansson-ard]

Review done, now it's @kateryna-lukina's turn!

[kateryna-lukina]

Reviewed, good job 🙌

[karlsoderby]

Hey @Hannes7eicher , some feedback regarding this article:

• At the moment it explains what Bluetooth is very well, but does not focus much on how it actually works with an Arduino board.
• It switches focus at the Arduino BLE Library section, but this is actually the start of a tutorial for how to use BLE with the MKR WiFi 1010. I think here the rework is needed so that it works on any device, including UNO R4 WiFi, Nano BLE, etc etc.
• The Arduino BLE Library section should not be very long, it should introduce the library briefly, link to the library, and link to the repository.
• There is no section that lists out the compatible boards. This should be at the top of the article. See this article for inspiration.
• Instructions are showing how to install a library using the Arduino IDE 1. I don't think we need to show how to install a library (we got some feedback on this recently), but if necessary, we should at least show the IDE 2, or link to the "install library" article.
• The last for sections Arduino BLE Library, Complete Code, Testing it Out & Conclusion are essentially linked together but in a guide like this it does not work. Each section should be more "standalone". In this case, I would rather see a single example per section. Like this:

---

Control LED Example

Short description, just a paragraph.

code example 

Expected outcome, again just paragraph, maybe a photo/gif/screenshot of terminal.

Another Example (maybe streaming sensor data?)

...

---

[karlsoderby]

Looking good @Hannes7eicher , left some suggestions and a comment about adding a circuit. Great work!