HVCAEN: Password management

Currently, in the HVCAEN and HVCAENA we are using the default username/password which is available in git for all to see. As a user and a dev, I would like my system to not have currently in use passwords available to the public. This may be the case in other drivers.

This ticket is to request a change of passwords on the CAEN and make it so that the two HVCAEN IOCs load the username/password from a secure location. The mechanism for loading the password from a secure location should be generalisable to other IOCs.

#### Acceptance criteria:

- [ ] Change of passwords requested
- [ ] HVCAEN and HVCAENA IOCs load the username and password from a secure location
- [ ] Mechanism to load passwords from a secure location is generalisable for other IOCs to use it

#### Notes:

- There is a private repo for password storage
- Have the private repo as a submodule
- There should be some kind of script/support module that pulls the passwords out of the repo and set as a macro/environment variable
- The macro/environment variable can then be read by the IOC