Updates to signing and distribution methods

[MonicaG]

Some minor updates to the documentation:

• Apple app signing
  • Updated the secret key names. They were updated in the bcgov GitHub org to make the names clearer to their purpose. Updated the documentation to reflect that change
• Distribution methods
  • Added in a sentence reflecting that both OCIO Mobile Device and Developer Experience teams need to take steps in setting up an internal app for distribution
  • Added headers to sections to help break up the content
• Google app signing
  • Added documentation on how to regenerate an upload key

The linked pages contain the updates on the dev site.