Fixed incorrect field assignment in Offers

[nebby2105]

#1092

• Removed duplicated values for languages, proficiencyLevel, userStatusEnum by replacing inline enum definitions with a reusable schemas.

• Created a new schema categoryWithAppearance and replaced the category property with a reference to it.

• Created a new schema offerAuthorExtended and replaced the author property with a reference to it (in offers).

• Created a new schema subjectWithName and replaced the subject property with a reference to it.

• Updated the FAQ property schema to include an _id field in each FAQ item.
• Updated the chatId property to also accept null, in addition to the string value.
• Updated the enrolledUsers property to use an array of strings instead of a reference to #components/user
• Created a new offerAuthor schema and replaced the author property with a reference to it (in offer).
• Updated example data for better representation of the API response.
• Removed unnecessary reference ($ref or ref) to other schemas where needed

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[ShadowOfTheSpace]

Great job!

[dudchakk]

amazing work! just please remove story points from PR title, they are supposed to be in the task title :)