config: rename allow_archive to allow-archive
As part of ConfigConsolidationPlan [1], rename the option according to
the new UI guidelines [2] and add an alias for backward compatibility.
[1]: https://www.mercurial-scm.org/wiki/ConfigConsolidationPlan
[2]: https://www.mercurial-scm.org/wiki/UIGuideline#adding_new_options
$ hg init
$ echo a > a
$ hg ci -Am t
adding a
$ hg mv a b
$ hg ci -Am t1
$ hg debugrename b
b renamed from a:b789fdd96dc2f3bd229c1dd8eedf0fc60e2b68e3
$ hg mv b a
$ hg ci -Am t2
$ hg debugrename a
a renamed from b:37d9b5d994eab34eda9c16b195ace52c7b129980
$ hg debugrename --rev 1 b
b renamed from a:b789fdd96dc2f3bd229c1dd8eedf0fc60e2b68e3