Migrate application from RMB and Vert.x to Spring stack

Purpose/Overview:
Since there is a general decision across Folio to move towards Spring Way and because of the module simplicity it's a good time to migrate module's source code to Spring. This will also save time in future by ignoring mandatory upgrades to new version of RMB per release.

mod-password-validator can be used as a reference implementation:
https://github.com/folio-org/mod-password-validator/tree/master/

Requirements/Scope:

1. API definition has to be described with OpenAPI
2. module's source code has to be migrated to Spring stack libraries

Approach:
See the sub-tacks for detailed description of what needs to be done (TBD)

Acceptance criteria:

• dependency to RMB is removed, the source code is based strictly on Spring libs
• the project can be built
• the existing unit tests are passing