Update Salesforce logo for OAuth

What does this MR do and why?

Updates the Salesforce logo that appears in the OAuth button on the sign-in page.

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. In the gitlab.yml file add the following around line 902 (under providers:):

   - { name: 'salesforce',
          # label: 'Provider name', # optional label for login button, defaults to "Salesforce"
          app_id: 'SALESFORCE_CLIENT_ID',
          app_secret: 'SALESFORCE_CLIENT_SECRET'
      }

2. Run GDK and go to the sign-in page.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #339579