Feat: Dex config migration

[vikramdevtron]

Description

Dex changes - configuration moves from argocd config map to devtron secret

Fixes # (issue): #2330

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How Has This Been Tested?

• SSO login with new configuration
• SSO login with existing configuration migration

Checklist:

• The title of the PR states what changed and the related issues number (used for the release note).
• Does this PR require documentation updates?
• I've updated documentation as required by this PR.
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have tested it for all user roles
• I have added all the required unit/api test cases