[POLICY] Change API and PAP usernames

- change references of healthcheck to policyadmin regarding API and PAP auth
- add robot variables to accommodate the referred changes.

Issue-ID: POLICY-3815
Change-Id: I318b7f44d9e7f554d98d845abd80cc6512831b78
Signed-off-by: adheli.tavares <adheli.tavares@est.tech>
8 files changed