refactor!: Rename AutolinkOptions to CreateAutolinkRequest, AddAutolink to CreateAutolink, and pass the body by value

[JamBalaya56562]

Continues the request-body-by-value work in #3644, this time for RepositoriesService.AddAutolink.

What changed

• AutolinkOptions is renamed to CreateAutolinkRequest, following the ...Request convention for request bodies. The old name was in the body-allowed-wrong-names allowlist.
• AddAutolink is renamed to CreateAutolink to match the docs operation name, Create an autolink reference for a repository. The doc comment already read "creates an autolink reference".
• The request body is now passed by value, and both AutolinkOptions entries are removed from the .golangci.yml allowlists.
• key_prefix and url_template are required by the API, so KeyPrefix and URLTemplate become non-pointer string without omitempty. is_alphanumeric is optional (it defaults to true), so IsAlphanumeric stays *bool.

Notes

• The request schema has exactly these three properties, so nothing was missing from the Go struct and no field needed to be added.
• The response type Autolink is a separate struct and is unchanged — this is a request-only type, so there is no create/update split to consider.
• test/integration/repos_test.go builds under the root module with -tags integration, so it is updated too. Its comparison needed a small fix rather than a mechanical rename: it compared actionlink.KeyPrefix (*string) against the request field, which is now a string, so it goes through GetKeyPrefix()/GetURLTemplate() instead.

Verified with go build ./..., go vet -tags integration ./test/integration/, gofmt, the full ./github/ test suite (CreateAutolink and the regenerated accessors at 100%), and custom-gcl (no paramcheck findings after removing the allowlist entries).

Updates #3644

BREAKING CHANGE: AutolinkOptions is renamed to CreateAutolinkRequest with non-pointer KeyPrefix and URLTemplate; RepositoriesService.AddAutolink is renamed to CreateAutolink and now takes the request body by value.

cc @jvm986 — flagging for #3644 coordination; this one is in the repos service, so it shouldn't overlap with the Issues work.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.52%. Comparing base (9549a7a) to head (c08e440).

Additional details and impacted files

@@ Coverage Diff @@## master #4399 +/- ##
=======================================
Coverage 97.52% 97.52% =======================================
Files 193 193 Lines 19668 19668 =======================================
Hits 19182 19182 Misses 268 268 Partials 218 218 

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[gmlewis]

Thank you, @JamBalaya56562!
LGTM.
Awaiting second LGTM+Approval from any other contributor to this repo before merging.

cc: @stevehipwell - @alexandear - @Not-Dhananjay-Mishra