TI API: Rel 0.9.9

[FabrizioMoggio]

This PR address the following problems:

• The TI API adopts 3Legs for any endpoints while sensitive data are not always exchanged.
• The description of the usage of the API for "user mobility" related scenarios is not good enough.
• The TI API doesn't not consider the phone number retrieved from the access token
• The TI API is not compliant with the CAMARA Guidelines in terms of Error Codes
• The callback is not compliant with Cloud Event

What type of PR is this?

Add one of the following kinds:

• bug
• correction
• enhancement/feature
• cleanup
• documentation

What this PR does / why we need it:

• This PR modifies the TI API adopting 3Legs only when sensitive data are exchanged.
• This PR improve the API documentation better explaining how to use the API in "user mobility" scenarios
• This PR consider the phone number retrieved from the access token
• This PR adds the missing Error Codes
• This PR implements the callback as Cloud Event

Which issue(s) this PR fixes:

• User mobility problem: TI API: user mobility problem #314
• 3Legs problem for optional parameter: TI API: 3Legs problem for optional parameter #246
• Phone number from access token: TI API: phone number from access token #284
• Error codes update: TI API: error codes update #320
• Cloud Event notification: TI API: Cloud Event notification #283

[FabrizioMoggio]

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