e2undo: add page (#5074)

pages/linux/e2undo.md

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+# e2undo
+
+> Replay undo logs for an ext2/ext3/ext4 filesystem.
+> This can be used to undo a failed operation by an e2fsprogs program.
+> More information: <https://man7.org/linux/man-pages/man8/e2undo.8.html>.
+
+- Display information about a specific undo file:
+
+`e2undo -h {{path/to/undo_file}} {{/dev/sdXN}}`
+
+- Perform a dry-run and display the candidate blocks for replaying:
+
+`e2undo -nv {{path/to/undo_file}} {{/dev/sdXN}}`
+
+- Perform an undo operation:
+
+`e2undo {{path/to/undo_file}} {{/dev/sdXN}}`
+
+- Perform an undo operation and display verbose information:
+
+`e2undo -v {{path/to/undo_file}} {{/dev/sdXN}}`
+
+- Write the old contents of the block to an undo file before overwriting a file system block:
+
+`e2undo -z {{path/to/file.e2undo}} {{path/to/undo_file}} {{/dev/sdXN}}`