CCSDK-2752: Examine DPS SPI and propose CPS Spike

Study the existing SPI used in ENM to migrate from Versant to ENM implementation. 

(TBA link to new GitHub repo with shared)

Learning from this SPI can be used to propose an SPI for the CPS SPI that also allows to 'plug-in' different DBs

1. Interface with Tony Finnerty for direction
2. ONAP Wiki Page describing
   1. High level structure of ENM SPI
   2. Already implemented SPI methods (from PoC)
   3. Suggestions for future structure & functionality
3. Discuss with Team and agree proposal

Jira Ticket:

CCSDK-2871 - DP: Agree and document proposed long-term Java API(s) IN PROGRESS

Jira Backlog:

https://jira.onap.org/secure/RapidBoard.jspa?rapidView=223&view=planning.nodetail&selectedIssue=CCSDK-2912&issueLimit=100

CPS Persistence SPI

https://github.com/Ericsson/cps-persistence-spi/tree/spi-docs/docs/dps-core-spi

CCSDK-2756 DM: [Spike] Propose C&PS Data Model#1.1.2Modelstore

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