mcp: add integration tests

[bobbyiliev]

Fixes: https://linear.app/materializeinc/issue/DEX-5/mcp-integration-tests

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[mtabebe]

I don't really have context on the rest of this change, but this change here seems fine to me...

[def-]

I'm wondering if we'd gain anything from testing from outside of cargo test. How slow is the cargo test execution btw?

[bobbyiliev]

I'm wondering if we'd gain anything from testing from outside of cargo test. How slow is the cargo test execution btw?

@def- ah yes good idea! The cargo tests run in-process so an external e2e test would definitely cover different ground. Will do a follow-up PR for that.

For cargo test speed, tests take about 3-9s each in CI:

PASS [   3.218s] (146/239) mz-environmentd::server test_mcp_agents_disabled
PASS [   5.302s] (147/239) mz-environmentd::server test_mcp_agents
PASS [   3.467s] (148/239) mz-environmentd::server test_mcp_agents_runtime_flag_toggle
PASS [   4.171s] (149/239) mz-environmentd::server test_mcp_agents_query_tool
PASS [   3.624s] (150/239) mz-environmentd::server test_mcp_observatory
PASS [   8.199s] (153/239) mz-environmentd::server test_mcp_agents_rbac
PASS [   9.025s] (156/239) mz-environmentd::server test_mcp_agents_with_data_product