Adding archive of previous versions of OpenConfig models.

[aashaikh]

Since vendor implementations will likely need to support earlier versions of module than the latest in the repository, it would be useful to publish earlier versions to make it easy to find them.

[aashaikh]

@robshakir PTAL at the structure of the model archive to see if it makes sense to pull into the public repo.

[robshakir]

A few questions on this one:

• In some cases e.g., FIB, we moved from models/fib to models/aft. It seems like we should keep a common directory even in the case that we have multiple different models within the same dir.
• What do we do in the case that we deprecate a model? (e.g., RPC) Do we need something that lets us specify the status of the model? Can we potentially have a top-level archive/models/<modelname>/.status file that stores this metadata?
• openconfig-types has acquired its own directory here, should we just move this into the types directory, and make this change in the normal public repo?

Otherwise, LGTM! Thanks for this!

[robshakir]

Another question - optical transport looks like this:

./optical-transport/0.1.0
./optical-transport/0.1.0/openconfig-optical-amplifier.yang
./optical-transport/0.1.0/openconfig-terminal-device.yang
./optical-transport/0.1.0/openconfig-transport-line-common.yang
./optical-transport/0.1.0/openconfig-transport-types.yang
./optical-transport/0.1.0/openconfig-wavelength-router.yang
./optical-transport/0.1.1
./optical-transport/0.1.1/openconfig-terminal-device.yang
./optical-transport/0.1.1/openconfig-transport-types.yang
./optical-transport/0.2.0
./optical-transport/0.2.0/openconfig-terminal-device.yang
./optical-transport/0.2.0/openconfig-transport-types.yang
./optical-transport/0.3.0
./optical-transport/0.3.0/openconfig-terminal-device.yang
./optical-transport/0.3.0/openconfig-transport-types.yang
./optical-transport/0.3.1
./optical-transport/0.3.1/openconfig-terminal-device.yang
./optical-transport/0.3.1/openconfig-transport-types.yang
./optical-transport/0.4.0
./optical-transport/0.4.0/openconfig-terminal-device.yang
./optical-transport/0.4.0/openconfig-transport-types.yang

So we end up looking like there is an optical-transport version 0.4.0 that removed things. Should we rather split the archive based on the model that is defined in .spec.yml.

Is there any reason that we shouldn't have .spec.yml files in public?

[aashaikh]

yeah, my thought here was that this is simply individual modules organized by version -- does not try to represent whole models. we would just explain that these directories are not 'cumulative' -- So a 'missing' file in a give directory just means that it only exists at some version numbers.

I thought a bit about spec files and concluded they were more relevant for our internal tooling; we can reconsider if we think they are useful for external folks. Using them to operate on the public repo should still be possible by accessing the spec file for a subdir from the release branch, for example.