OIDC configuration option for label of "OpenID" button

[oxdef]

Steps to reproduce:

1. Enable OIDC
2. Navigate to DependencyTrack login page

Current Behavior:

See additional button with icon and label "OpenID"

Proposed Behavior:

It is a typical case to use OIDC as SSO solution and will be clear to the end user see on this button custom text, e.g. "Log in as Company employee". So it's good to make this text configurable via OIDC frontend config (https://docs.dependencytrack.org/getting-started/openidconnect-configuration/).

[oxdef]

Made PR for this issue: #80