Car docs: update alpha longitudinal name (#29670)

* Update Footnote 1

Updated Footnote 1 for new name for toggle "openpilot Longitudinal Control (Alpha)" as well as made it clearer on how to change to devel or master-ci branches, taken from comma.ai blog (https://blog.comma.ai/090release/#experimental-longitudinal-control).

* Add 3X

* Added to Docs_definitions

* just update name

* fix

* fix

---------

Co-authored-by: Shane Smiskol <shane@smiskol.com>

docs/CARS.md

@@ -268,7 +268,7 @@ A supported vehicle is one that just works when you install a comma three. All s
 |Volkswagen|Touran 2016-23|Adaptive Cruise Control (ACC) & Lane Assist|openpilot available[<sup>1,12</sup>](#footnotes)|0 mph|0 mph|[![star](assets/icon-star-full.svg)](##)|[![star](assets/icon-star-full.svg)](##)|<details><summary>Parts</summary><sub>- 1 J533 connector<br>- 1 USB-C coupler<br>- 1 comma three<br>- 1 harness box<br>- 1 long OBD-C cable<br>- 1 mount<br>- 1 right angle OBD-C cable (1.5 ft)<br><a href="https://comma.ai/shop/comma-3x.html?make=Volkswagen&model=Touran 2016-23">Buy Here</a></sub></details>||
 
 ### Footnotes
-<sup>1</sup>Experimental openpilot longitudinal control is available behind a toggle; the toggle is only available in non-release branches such as `devel` or `master-ci`.  <br />
+<sup>1</sup>openpilot Longitudinal Control (Alpha) is available behind a toggle; the toggle is only available in non-release branches such as `devel` or `master-ci`. <br />
 <sup>2</sup>By default, this car will use the stock Adaptive Cruise Control (ACC) for longitudinal control. If the Driver Support Unit (DSU) is disconnected, openpilot ACC will replace stock ACC. <b><i>NOTE: disconnecting the DSU disables Automatic Emergency Braking (AEB).</i></b> <br />
 <sup>3</sup>Refers only to the Focus Mk4 (C519) available in Europe/China/Taiwan/Australasia, not the Focus Mk3 (C346) in North and South America/Southeast Asia. <br />
 <sup>4</sup>Requires a <a href="https://github.com/commaai/openpilot/wiki/GM#hardware" target="_blank">community built ASCM harness</a>. <b><i>NOTE: disconnecting the ASCM disables Automatic Emergency Braking (AEB).</i></b> <br />

selfdrive/car/docs_definitions.py

@@ -176,7 +176,7 @@ CarFootnote = namedtuple("CarFootnote", ["text", "column", "docs_only", "shop_fo
 
 class CommonFootnote(Enum):
   EXP_LONG_AVAIL = CarFootnote(
-    "Experimental openpilot longitudinal control is available behind a toggle; " +
+    "openpilot Longitudinal Control (Alpha) is available behind a toggle; " +
     "the toggle is only available in non-release branches such as `devel` or `master-ci`.",
     Column.LONGITUDINAL, docs_only=True)
   EXP_LONG_DSU = CarFootnote(