fix: add :enabled sub-config for fixer tools
This allows distributing opt-in fixer tool configurations in .hgrc
files. This may be useful for adding default configs in core, or for
orgranizations that want to provide configs to their users.
Tools are still enabled by default because it would be confusing to add a
config and find that it has no effect until you add enabled=true.
Differential Revision: https://phab.mercurial-scm.org/D6975
-----BEGIN CERTIFICATE-----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-----END CERTIFICATE-----