Add EGO public key fetching at boot

[rtisma]

Currently, the EGO public key is configured via env variable. This means, the person deploying dms-ui needs to:

• call the ego public key endpoint
• extract the public key from the response
• update the dms-ui qa and staging helm values
• make a PR
• get someone to review the PR
• merge pr
• redeploy the new public key

It would be better if instead dms-ui required EGOs public key url, and then on boot, it fetches the public key and uses that. If the public key changes, instead of going through the complicated steps above, the dms-ui just needs to do a rolling restarts (i.e k rollout restart deploy/dms-ui). This significantly simplifies the deployment process

[b-f-chan]

After discussing with @anncatton and cnosultation with @hlminh2000 , it seems the EGO public key is actually currently NOT used at all in the DMS-UI code. The config is in the helm chart but is not required for any functionality. In the future, if we implement access control, this may be required, but for now it leads to confusion during deployment. Suggestion is to remove it from the DMS-UI code and the Helm chart config.

At minimum, we'll backlog it and discuss with @rtisma, but this will not be included in the next sprint.