[DOC] Update Pyroscope for Agent > Alloy about pyroscope HOT 2 OPEN

From #3381:

This change will disable the agent by default and enable alloy instead.

Fixes #3282

This is breaking change for all helm chart users.

It is required that their custom options are either migrated by replacing agent with alloy or they maintain the previous behaviour by agent.enabled: true alloy.enable: false

from pyroscope.

Feedback from Ashley for the install docs for Pyroscope based on a customer's feedback:

• grafana agent referenced frequently which confused the prospect
• as a suggestion, it would be easier if the components were named the same so as we're copy/pasting from the different sections it will work without changes
  • EX - all the full examples in this page have a local pyro as the write output (even though its called send to cloud), but if you copy the cloud profiles config at the top this component is called endpoint while the rest of the sample config writes to example
• this page references and installs the grafana agent, not alloy - is it intentional? with a new prospect they have already installed alloy, so this is confusing if they want to just add the relevant config lines and also agent is being deprecated soon
• I think it would be helpful to have a tab answering 'what if im running opentelemetry collector' since this is what most (of my) prospects are using
• it would be helpful if the helm chart or instructions to install alloy were at the beginning of the instructions, since it doesn't list as a pre req that you need to first install it
• from the cloud profiles doc when you start to follow the instructions to configure it brings you to the oss docs. So my prospect clicked into "Deploy on K8s" thinking it would be what he needed, but these are instructions to deploy actual pyro.

from pyroscope.