Support import records from excel file

[blcham]

Variants of excel import:

• Standard variant of excel import -- the external service creates records in json which are then imported by backend.
• Detached variant of excel import -- the external service deploys newly created records directly to database instead of returning it to the backend.

A/C:

• if external service for import of excel is configured it should be called on the import button
• if external service is not configured it should behave as before
• detached variant of excel import is implemented by default

[blcham]

Inspire by PRs.

• for enviroment variable setup -- Add publish rest api record-manager#56
  • PUBLISH_SERVICE_URL("publishServiceUrl"), --> EXCEL_IMPORT_SERVICE_URL
• how to call external API -- take the current state of files referenced by
  • backend -- https://github.com/kbss-cvut/ava-analytics/pull/38
  • frontend -- https://github.com/kbss-cvut/ava-analytics-ui/pull/59, https://github.com/kbss-cvut/ava-analytics-ui/pull/60

[blcham]

@palagdan Make sure that you can do the following:

• test backend in the deploy/keycloak-auth deployment
• debug backend within the deploy/keycloak-auth deployment
• setup you backend to existing frontend so it can be tested