Feat: Automatically detect signing certificate

[shehan-bb]

What does this PR do

Adds the capability to retrieve the signing certificate name from the Keychain if exists from the team id provided.

How can it be tested

Use a TeamID of a signing certificate present in the keychain access in the properties and see if the correct certificate name is populated in the xcodeproj file after variants switch command

Task

resolves #239

Checklist:

• I ran make validation locally with success
• I have not introduced new bugs
• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented on my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new errors

[GMinucci]

With this approach we will always try first to set automatically which could break in case the first cert is not valid anymore. Let's make this a new feature that can be enabled so we avoid breaking previous versions.
This is an example of

signing:
    ...
    codesign_identity: <option> 

And the options could be:

1. auto_detect_system -> This uses the new mechanism, fallback to option 2 if cant find any
2. auto_name -> This is the previous approach (make this the default)
3. user inputted value -> This should set whatever the user set in the configuration for full control

What are your thoughts on this @shehan-bb @arthurpalves ?

[shehan-bb]

With this approach we will always try first to set automatically which could break in case the first cert is not valid anymore. Let's make this a new feature that can be enabled so we avoid breaking previous versions. This is an example of

signing:
    ...
    codesign_identity: <option> 

And the options could be:

1. auto_detect_system -> This uses the new mechanism, fallback to option 2 if cant find any
2. auto_name -> This is the previous approach (make this the default)
3. user inputted value -> This should set whatever the user set in the configuration for full control

What are your thoughts on this @shehan-bb @arthurpalves ?

Yes, this can be useful to avoid any unexpected behaviour.