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_