Update the Package.md validation done when pushing a bala to the BC

[azinneera]

Current Limitation

With the improvement ballerina-platform/ballerina-lang#42981, the BALA files can contain a different file than Package.md. The validation should be updated to support both formats.

Suggested Improvement

In the new format, the readme file must be taken from the package.json file.

E.g. package.json

{
  "organization": "asmaj",
  "name": "doc2",
  "version": "0.1.0",
  "export": [
    "doc2"
  ],
  "ballerina_version": "2201.11.0-SNAPSHOT",
  "implementation_vendor": "WSO2",
  "language_spec_version": "2024R1",
  "platform": "any",
  "graalvmCompatible": true,
  "template": false,
  "readme": "docs/Package.md" // new field
}

For old balas, we should keep the current validation; for the new ones, the validation should be updated. To identify if the bala is of the old format or the new one, the bala.json file can be used. The bala_version field in the old one is 2.0.0 whereas the one in the new format is 3.0.0

E.g:
Old bala.json:

{
  "bala_version": "2.0.0",
  "built_by": "WSO2"
}

New bala.json

{
  "bala_version": "3.0.0",
  "built_by": "WSO2"
}

Version

No response