Allow gitlab_project_label name updates without replacement

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This change updates the gitlab_project_label resource to allow updating the name attribute without forcing resource replacement, which previously caused labels to be removed from issues and MRs.

Changes:

• Changed resource ID format from : to :<label_id>
• Removed RequiresReplace() from name attribute schema
• Updated CRUD operations to use label ID instead of label name
• Modified Update function to use NewName parameter for renaming
• Added automatic state migration from V1 to V2 format
• Added test case to verify label renaming works without replacement
• Updated documentation to reflect new ID format

The implementation follows the same pattern as gitlab_group_label and ensures that renaming labels preserves their associations with issues and merge requests.

Fixes: #6356 Signed-off-by: VijetaPriya47 vijeta004@gmail.com