Deployment lesson: Update railway's free plan details

[vs-yashwanth]

Because

The current description of Railway's free trial plan in the Deployment lesson is not consistent with Railway's own documentation.

This PR

• Changed the description of Railway's free plan from saying "500 one time use hours" to "5$ one time grant"
• Mentioned that the longevity of the free trial grant is usage based.

Issue

Closes #26316

Additional Information

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[KevinMulhern]

Thanks for taking the time to do this @srivathsa-yashwanth, would you mind making the same change to the Rails version of this lesson?

[vs-yashwanth]

Not at all, I will add that commit to this PR 😊