Improve uuid usage in bal persist learn page

[HindujaB]

Description

$subject

The persist learn page uses an Employee record to add to the data store.
https://ballerina.io/learn/manage-data-persistence-with-bal-persist/#create-a-new-employee-record

The provided sample uses uuid:createType4AsString() to create a unique id. And in the samples that follow it uses a hard-coded string as an id to retrieve/modify/delete the record entries.
https://ballerina.io/learn/manage-data-persistence-with-bal-persist/#retrieve-the-employee-record-by-key

As the generated id can differ randomly, the further samples can fail which may confuse the user.
Similar to the other learn pages, it's better to provide a step-by-step approach to the users where the code context can be gradually developed.

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[praneesha]

The fix will be changed via #8230.

[praneesha]

Closing as the change is done via #8230.