Add version number to the seeder
Add version number to the seeder

Summary:
The seeder does not currently have a version number.  This will make it
easier to direct users to upgrade.

Test Plan:
  ninja
  ./bitcoin-seeder --version
Verify the output is as follows (or similar if version changes before this lands):
  Bitcoin ABC Seeder v0.21.4-2436d3037
  ./bitcoin-seeder --help
Verify that the version output above appears before the rest of the help text.

Reviewers: O1 Bitcoin ABC, #bitcoin_abc, deadalnix

Reviewed By: O1 Bitcoin ABC, #bitcoin_abc, deadalnix

Subscribers: deadalnix

Differential Revision: https://reviews.bitcoinabc.org/D5617

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