Provide script to upload agreements into an Integration Account

[mbraekman]

Is your feature request related to a problem? Please describe.
In order to be able to upload agreements (1 agreement per JSON-file) into an Integration Account, this either has to be done manually or some custom scripts. Allowing to set up AS2, EDIFACT or X12 agreements between partners.
Since there is already a script that offers this functionality (in a bigger picture) we can extract the logic to upload agreements into a separate script.
This allows users to either only upload agreements, or run the larger command to upload all available Integration Account artifacts.

The given script uses the REST API since no scripts were available yet at the time, or it had severe limitations.
To be checked whether this can be replaced by the following commands:

• New-AzIntegrationAccountAgreement
• Set-AzIntegrationAccountAgreement

Describe the solution you'd like
The script should accept the following parameters:

• IntegrationAccountName
  The name of the Integration Account to be targetted.
• IntegrationAccountResourceGroup
  The name of the resource group containing the Integration Account
• AgreementsFolder
  Folder containing all JSON files describing the agreements to be created.
• ArtifactsPrefix (optional)
  When present, add this prefix to the name of the agreements before uploading (in case of sharing an Integration Account across multiple environments in order to save costs.

Additional context
This is part of a number of scripts to upload artifacts into an Azure Integration Account, in order to replace the Integration-DeployIntegrationAccountArtifacts.ps1 from the Invictus Templates.