Add custom headers to Custom MCP adds to allow for customer headers x-api-key

### Problem Statement

I am trying to connect marketingsecrets.ai to give access to my voice, writing, assets, etc but they only offer custom header x-api-key info to connect, not OAUTH

### Proposed Solution

add custom headers under advanced setting to add custom MCP

### Alternatives Considered

_No response_

### Area

MCP Connector (adding/managing servers)

### Priority

Critical - Blocking my MCP server development

### Additional Context

_No response_

Start by reviewing the MCP Connector area for the flow that adds and manages custom servers, then locate the advanced settings mentioned in the proposal. The work is complete when a custom MCP can accept and use an x-api-key custom header for connections that do not offer OAuth.

Vom Indexierungsmodell aus dem Issue-Text verfasst.