Documentation Version Structure Update

We have introduced a new version structure for our Firmware documentation to make it easier to find information about new features and ongoing development.

Previously:

• Documentation was split into stable, testing, and nightly versions.
• It was often confusing to locate details about new or upcoming features.

Now:

• Documentation is organized into stable and devel versions.
• All unfinished features and ongoing development are documented in the devel section.
• Once a firmware release is finalized and becomes stable, the related documentation is moved from devel to stable.

This change makes it clear where to find information about new features: if it's not finished, it's in devel; if it's released, it's in stable. This should help everyone stay up to date and avoid confusion about where to look for the latest updates.