Connector reference pages for SharePoint Online and Confluence don't mention Elastic-managed (agentless) availability

## Problem
The reference pages for the **SharePoint Online** and **Confluence** connectors state the
connector is "available as a self-managed connector" and do not mention that it can also be
set up as an **Elastic-managed (agentless)** connector. But the Kibana Content Connectors
"Create connector" wizard on Elastic Cloud Hosted offers **Elastic managed** as a setup
option for both.

## Pages affected
- https://www.elastic.co/docs/reference/search-connectors/es-connectors-sharepoint-online
- https://www.elastic.co/docs/reference/search-connectors/es-connectors-confluence

(Other connector reference pages may have the same gap; these are the two I verified.)

## What the docs say
Each page's "Availability and prerequisites" section says the connector "is available as a
self-managed connector," with no mention of an Elastic-managed / agentless option.

## What the product actually does
On Elastic Cloud Hosted (observed on stack **9.4.3**):
Stack Management → Content Connectors → Create connector → select **SharePoint Online** or
**Confluence Cloud & Server** → the **Setup** step shows **"Elastic managed"** and
**"Self-managed"** radio options. "Elastic managed" is selectable and provisions an
agentless deployment.

## Why it matters
Readers choosing between managed and self-managed rely on these pages. Because they mention
only self-managed, it's easy to wrongly conclude Elastic-managed isn't supported for these
sources, when the UI clearly offers it.

## Suggested fix
In each connector reference page's "Availability and prerequisites" section, state whether
the connector is available as **Elastic-managed (agentless)** in addition to self-managed,
and in which environments (Elastic Cloud Hosted / Serverless). A single canonical table
mapping "Elastic-managed vs self-managed" per connector would remove the ambiguity.

## Environment
- Elastic Cloud Hosted, stack 9.4.3
- Kibana Content Connectors "Create connector" wizard

Open the SharePoint Online and Confluence connector reference pages and inspect their “Availability and prerequisites” sections. Update both pages to document Elastic-managed (agentless) availability alongside self-managed, including the supported Elastic Cloud Hosted or Serverless environments described in the issue; done means readers can distinguish the two setup options.

Written by the indexing model from the issue text.