Install migrator and migration helpers

[sam-aws]

Issue #, if available:
#90

Description of changes:
Install the migrator tool and individual migration helpers into the
image. This defines a 'migration' package that must be required-by the
release package, and extends the cargo_install macro to optionally
specify the root directory.
Migration versions are only specified in the install for-loop at the
moment, but otherwise are automatically handled by populating a
migration-binaries file to use with %files -f

Signed-off-by: Samuel Mendoza-Jonas samjonas@amazon.com

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[sam-aws]

This mostly addresses #90, with some points worth discussing:

• Defining which migrations to install
  Right now this is just a list of versions defined in the %install step which are then iterated over, but depending on how often this is updated there may be a more user friendly location to define it.

• All migrations are built unconditionally.
  Because the api %build step is just %cargo_build --all all migrations are built regardless if they will be installed. Unless the number of migrations gets truly out of hand this is probably fine but worth pointing out.

• Migration workspace & naming
  At the moment there's only the v1.1/testmigration migration as an example, but i
  t sounds like we probably expect a list of potential migration projects like:

v1.1/foo
v1.1/bar
v1.2/foo

So we'd also need to decide on a list of migration names per version, unless we unconditionally install every migration for a given version.

[tjkirch]

we'd also need to decide on a list of migration names per version, unless we unconditionally install every migration for a given version.

Assuming we want migrations for version X, we'd want every migration under X. The names are just there for the developer of the migration to briefly explain their purpose. Anything tagged to a specific version is expected to be required for that version.

[tjkirch]

Nice! What do you think is left before merging? I could probably help test the branch.

[bcressey]

LGTM