POC cocoapod-keys for secrets management

[glm4]

Description:

• This PR is a POC for using cocoapod-keys plugin for secrets management.
• Currently the keys are set from the Environment during the pre phase of pod install. This avoids the command to request each individual key. If that happens, it would be a sign that some key is missing from the configuration.

Limitations: Keys are global and running locally with a different build configurations will use the same keys.

One alternative is to have different keys per build configuration(which can be painful):

var apiClientSecret {
    #if $(CONFIGURATION) == 'Debug'
    return keys.testSecretDev
    #else
    return keys.testSecretProd
    #endif
}

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Notes:

• In explorations/TBD: How to configure Google-Info.plist with the keys depending on the current build configuration. There is currently a chicken-egg situation, where the secrets need to be set before pod install, but the configuration where the project is built is not known yet. The configuration is needed in order to fill up the plist file with the right keys.

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