Add custom headers to MCP Toolset in CES

[habh-11]

Release Note Template for Downstream PRs (will be copied)

See Write release notes for guidance.

ces: added `customHeaders` field to MCP toolset in CES `google_ces_toolset` resource

[github-actions]

Googlers: For automatic test runs see go/terraform-auto-test-runs.

@hao-nan-li, a repository maintainer, has been assigned to review your changes. If you have not received review feedback within 2 business days, please leave a comment on this PR asking them to take a look.

You can help make sure that review is quick by doing a self-review and by running impacted tests locally.

[modular-magician]

Hi there, I'm the Modular magician. I've detected the following information about your changes:

Diff report

Your PR generated some diffs in downstreams - here they are.

google provider: Diff ( 5 files changed, 55 insertions(+))
google-beta provider: Diff ( 5 files changed, 55 insertions(+))
terraform-google-conversion: Diff ( 1 file changed, 18 insertions(+))
Open in Cloud Shell: Diff ( 1 file changed, 3 insertions(+))

[modular-magician]

Tests analytics

Total tests: 50
Passed tests: 48
Skipped tests: 0
Affected tests: 2

Click here to see the affected service packages

• ces

Action taken

Found 2 affected test(s) by replaying old test recordings. Starting RECORDING based on the most recent commit. Click here to see the affected tests

• TestAccCESToolset_cesToolsetMcpServiceAgentIdTokenAuthConfigExample
• TestAccCESToolset_cesToolsetMcpServiceAgentIdTokenExample_update

Get to know how VCR tests work

[modular-magician]

🟢 Tests passed during RECORDING mode:
TestAccCESToolset_cesToolsetMcpServiceAgentIdTokenAuthConfigExample [Debug log]
TestAccCESToolset_cesToolsetMcpServiceAgentIdTokenExample_update [Debug log]

🟢 No issues found for passed tests after REPLAYING rerun.

---

🟢 All tests passed!

View the build log or the debug log for each test