Add Oracle compute metadata source provider

[Gabriel Samfira]

For the most part cloud-init can initialize an instance inside oracle compute using the EC2 metadata source provider.

There are however some aspects that do not work well, or at all. To mention just a couple:

* initializing multiple NICs
* fetching metadata when the first NIC is a VNIC intead of a VEthernet nic
* Userdata can be a valid JSON. While a simple string is also a valid JSON, if the user decides a hashtable is more suitable, cloud-init should be able to look for a specific key

Here is some more info on the matter:

https://docs.oracle.com/cloud/latest/stcomputecs/STCSG/GUID-C391125C-047A-4A77-BC96-8BF5E4BBE131.htm

[James Falcon (falcojr)]

Oracle has been a first class datasource since cloud-init 18.4

[James Falcon (falcojr)]

Tracked in Github Issues as https://github.com/canonical/cloud-init/issues/2841