Identify the Synthetic Agent as a Browser Type RUM

[paulb-elastic]

This specifically covers traffic generated by the Synthetic Agent, and does not for example include HTTP Ping hits from Heartbeat

As an Elastic Observability User
I want to be able to identify Synthetic traffic in the User Experience reporting
So that I can look at how real users vary compared with my Synthetic baseline
And I can exclude Synthetic monitors and see if they are skewing my performance data (subject to this)

Acceptance criteria

• Any interactions by the Synthetic Agent to my website that is being monitored by the RUM Agent, can be distinguished from other organic traffic to the website
• I can select the “Synthetic Agent” as a variety of browser in the reporting (e.g. browser filter, page load distribution breakdown)
• Similarly, traffic from the Synthetic Agent will be categorised as the device type of ‘bot’ (may need some additional work around Categorise device type (phone/tablet/bots/etc) from User Agent String elasticsearch#65057 to support this)