Improve GCP and Azure credentials documentation

[CarlosRS9]

Description

We have reviewed the Azure and GCP integrations documentation regarding the differente authentication options available, focusing in the custom credentials file option. Prior to this change our documentation was not clear enough about how to use these options.

Here are some of the major changes that have been applied:

• Azure Authentication options
  • Azure credentials section renamed.
  • Added a new subsection explaining how to obtain the different credential values.
  • Expanded the existing documentation to clarify how to properly set up the credentials
  • Reviewed and improved configuration examples
• Configuring GCP credentials
  • Added a new subsection explaining the authentication method available
  • Minor fixes to the reference and configuration examples

Checks

• [x] It compiles without warnings.
• [x] Spelling and grammar.
• [x] Used impersonal speech.
• [x] Used uppercase only on nouns.
• [x] Updated the redirect.js script if necessary (check this guide).