Fixes the issue with Azure OpenAI Chat and OpenAI Chat connector when getting nullable values

[nadheesh]

Description

Fixes https://github.com/wso2-enterprise/choreo/issues/26615

Also we are removing deprecated tags from few records in openai.chat connector because, we are using that connector to release ai.agent module that deprecated tags can fail the release of that module.
(and migrating ai.agent module to updated API will require significant effort, which we will do in the future)

Fixes # (issue)
https://github.com/wso2-enterprise/choreo/issues/26615

One line release note:

• One line describing the feature/improvement/fix made by this PR

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Provide instructions so we can reproduce. Please also list any relevant details for your test configuration

• Tested manually

Test Configuration:

• Ballerina Version: 2201.8.4
• Operating System: Mac

Checklist:

Changes to OpenAPI definition

• Modified info section of the OpenAPI definition file - Example

  • description - what the connector is about
  • x-ballerina-init-description OpenAPI extension - connector initialization details
  • x-ballerina-display OpenAPI extension - connector name and path to the connector icon

• Added proper description each API Key, if API Key authentication is defined in OpenAPI definition file

Changes to connector module

• Added license header at the top of each .bal file.
• Added Package.md as per the guide here
• Added Module.md for the module of the connector as per the guide here
• Added connector icon to the root of the connector. Icon needs to be a png of 200x200 px size with name icon.png
• Added Ballerina.toml file with following information. For keywords refer to guide

Verifying connector module

• Compiled the connector successfully with the targeted ballerina version.
• Conducted smoke tests on the connector (Recommended when OpenAPI definition is obtain from an unofficial source)

Security checks

• Followed secure coding standards in http://wso2.com/technical-reports/wso2-secure-engineering-guidelines?
• Confirmed that this PR doesn't commit any keys, passwords, tokens, usernames, or other secrets?