Remove experimental label for `rasa data validate stories`

[TyDunn]

@JEM-Mosig and I agree that rasa data validate stories is a core part of test step of CDD, where you make sure that there are no conflicts in your stories before automated tests in a CI pipeline, and we should remove the experimental feature designation in the Rasa Open Source docs

https://rasa.com/docs/rasa/command-line-interface#rasa-data-validate

Definition of done

• Remove experimental warning in docs
• Remove the warning in the code
• Update the experimental feature table in Notion

[pranavdurai10]

@TyDunn @JEM-Mosig is this still open for contribution? If so, can I take over?

[TyDunn]

@pranavdurai10 Yes 👍

[alopez]

assignee: @aeshky
reviewer: @koernerfelicia

[aeshky]

Working branch: remove_exp_label.
Note: I could not find a warning in the code associated with rasa data validate stories.
Notion page updated: here.
Pull request:
#9194 this PR got too messy when I changed the target branch.
I created a new PR here: #9237