Expose Bitbucket Project Name / Slug as Pipeline Environment Variable

[Burak Morallı]

Currently Bitbucket Pipelines only exposes BITBUCKET_PROJECT_KEY.
This value is not suitable for human-readable identifiers such as SonarQube project keys, Docker image names, or Helm release names.

The project name or project slug is already available in the Bitbucket UI and through the REST API, but it is not exposed as an environment variable.

Providing a variable such as BITBUCKET_PROJECT_SLUG or BITBUCKET_PROJECT_NAME would greatly simplify CI/CD naming standards without requiring additional API calls or manually defined variables.

Use cases:
  - SonarQube project keys
  - Docker image naming
  - Helm release names
  - Logging and observability

Expected behavior:
  - A new optional environment variable exposing the project name or project slug
  - Clear documentation regarding mutability