feat(ngMessagesConfig): global configuration of the default value for ngMessages' multiple

[lili21]

#11797

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[lili21]

I signed it!

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CLAs look good, thanks!

[Narretz]

Hi, thanks for the PR. There a few things however that need to be changed before this can be added:

• app-wide configs should use providers instead of constants
• the behavior needs tests (e.g. if multiple is set when the config is set)

[gkalpak]

Closing due to lack of response.