Support upgrades with different binary hashes

[ptrus]

Currently the upgrade module supports a single upgrade type ("internal") which relies on binary hash to ensure correct node version for upgrade is used:

oasis-core/go/upgrade/api/api.go

Lines 71 to 73 in 5af6d91

	// Identifier is a hash of the binary to be used for upgrading.
	// Upgrade methods other than "internal" may have differently formatted identifiers.
	Identifier string `json:"identifier"`

We should stop using the hash of the binary to ensure correct version is running and instead use something like a software version. Otherwise upgrade will be hard to coordinate with people doing custom builds.

Can either create a new upgrade type or update (and rename?) the existing "internal" upgrade type to not rely on exact matching binaries - as that doesn't seem all that useful.

Should do after #3536 is merged, as that PR contains some significant changes to the upgrade module.

Also enforce unique upgrade descriptor names.

[kostko]

Can either update a new upgrade type or update (and rename?) the existing "internal" upgrade type to not rely on exact matching binaries - as that doesn't seem all that useful.

I would opt for reusing/renaming the existing upgrade type.