Context:
As more and more public APIs are added we decide to consolidate the accessToken(s) together into one shared config, see https://camunda.slack.com/archives/CNSMT82SJ/p1639386771001800

AT:

• a global accesstoken config is used by all public APIs of Optimize, see https://docs.camunda.org/optimize/develop/technical-guide/rest-api/
  • there is already an existing config property to be used being api.optimizeAccessToken
• the following accessToken configs are removed from the documentation:
  • eventBasedProcess.eventIngestion.accessToken
  • externalVariable.variableIngestion.accessToken
  • export.json.accessToken
• the following accessToken configs are marked as deprecated:
  • eventBasedProcess.eventIngestion.accessToken
  • externalVariable.variableIngestion.accessToken
• there is no automatic access token generation in case the value is set to `null` but instead api calls will be blocked (as already done for export.json.accessToken
• the documentation is adjusted accordingly