dev-docs (MCP server): Add tracing and errors documentation

[betegon]

DESCRIBE YOUR PR

Closes #14106

Adds developer docs for our MCP Server instrumentation.

Route for the documentation sdk/expected-features/mcp-instrumentation that includes:

.mcp-instrumentation
├── index.mdx  # brief description on current features and limitations
├── errors.mdx # draft errors doc 
└── tracing.mdx # Tracing and span conventions

Followed this file structure as a start to (in the future) have this structure for all the other features, having something like this below, where we have :

.[Feature 1]
├── index.mdx 
├── logs.mdx 
├── errors.mdx 
.
.
.
.[Feature 2]
├── index.mdx 
├── errors.mdx 
├── tracing.mdx
.
.
.

The structure idea is from @abhi, who helped me settle this <3.

NOTE: Error docs are going to change, addressing feedback from sentry-javascript/pull/16817

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[AbhiPrasad]

nice, this is what I think we want. Once we convert the errors spec to stop using tags we can merge!

[coolguyzone]

Looks good! Thanks for adding 🫡

[betegon]

Hey @coolguyzone , thanks for reviewing it. I was waiting to update the erors docs to use mechanism instead of tags. It's updated now, please have a look at it, this is the actual change 46958b.