fix(csharp): emit bare hostname for telemetry host_url to match JDBC

[jadewang-db]

Summary

driver_connection_params.host_info.host_url was emitted as "https://<host>:443", differing from JDBC which emits a bare hostname (e.g. host.cloud.databricks.com). Analysts joining on host across drivers had to normalize. Port is already reported separately in host_info.port (PECO-2982), so the scheme + :443 suffix served no purpose.

Change

csharp/src/Telemetry/ConnectionTelemetry.cs: emit bare host instead of $"https://{host}:{port}" for HostUrl.

Field	Before	After
host_info.host_url	"https://host.cloud.databricks.com:443"	"host.cloud.databricks.com"
host_info.port	443	443 (unchanged)

Test plan

• Added regression test ConnectionParams_HostInfoHostUrl_IsBareHostname in csharp/test/E2E/Telemetry/ConnectionParametersTests.cs verifying the host_url matches the bare hostname from connection properties.
• Updated existing ClientTelemetryE2ETests assertion from Assert.Contains("https://", ...) to Assert.DoesNotContain("://", ...).
• Updated csharp/doc/telemetry-design.md and docs/designs/fix-telemetry-gaps-design.md example payloads + validation rules.
• Full dotnet test --filter "FullyQualifiedName~Unit." suite: 638 passed.

Stack

This is the base of a 2-PR stack. PR #456 (PECO-3021, enable_fast_metadata_query) will be re-targeted onto this branch once merged.

Closes PECO-2987.

[jadewang-db]

Closing — discovered after opening that d02dae2 on this branch is content-identical to the already-merged squash commit 640fbbd from PR #401. The host_url bare-hostname fix is already on main; no separate stack PR needed. PR #456 will be re-targeted back to main.