Create PolicyExecutor Stub

Create PolicyExecutor Stub

- Generate interface from OpenApi in RTD docs
- Fixed Content Type in OpenAPI
- Fixed Paths in OpenAPI
- Made Authorization header compulsory in OpenAPI
- All 'enum' values in OpenAPI lowercase (in linr with CPS/NCMP conventions)
- Added impl with some basic functionality
- Added testware
- Pom includes docker image creation
- Docker compose updated to deploy stub

Issue-ID: CPS-2301
Change-Id: I462ad5c70474b2813fc04005c0d20a1b15b574ec
Signed-off-by: ToineSiebelink <toine.siebelink@est.tech>
Signed-off-by: sourabh_sourabh <sourabh.sourabh@est.tech>