fix: Update session handling to use a consistent session name

[dev-bre]

This pull request standardizes the session name used across authentication handlers and middleware by replacing the use of a configurable sessionSecret with the hardcoded string "trakrlog-session". This ensures consistent session management and simplifies session retrieval throughout the codebase.

Authentication session handling:

• Updated the session creation in GitHubHandler.HandleCallback to use "trakrlog-session" instead of the variable h.sessionSecret.
• Updated the session creation and retrieval in GoogleHandler.HandleCallback and GoogleHandler.GetAuthUser to use "trakrlog-session" instead of h.sessionSecret. [1] [2]

Middleware session retrieval:

• Modified the RequireAuth middleware in auth.go to use "trakrlog-session" for session retrieval instead of the passed sessionSecret parameter.…GitHub and Google handlers

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)
• Documentation update

Related Issue

Closes #(issue number)

How Has This Been Tested?

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Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes