git-rename-tag: add page

pages/common/git-rename-tag.md

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+# git rename-tag
+
+> Rename a Git tag.
+> Part of `git-extras`.
+> More information: <https://github.com/tj/git-extras/blob/master/Commands.md#git-rename-tag>.
+
+- Rename an existing Git tag locally and remotely:
+
+`git rename-tag {{old_tag_name}} {{new_tag_name}}`