tools: add dedup estimation tool bdedupestimate

[sebsura]

Thank you for contributing to the Bareos Project!

This pr adds a tool with which you can estimate how much space you could save when using deduplication.

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[pstorz]

Create a manpage for bdedupestimate please.

[pstorz]

Wouldn't it make sense to have a system test that runs bdedupestimate?

[pstorz]

• dedup factor format should be 2.34x (like ZFS does the output) and not x2.34. See comment
• Some commits still contain "Fixup"