fix(go): add some missing deprecations in compat layer (#243)

Author: rubenhoenle

languages/golang/compat-layer/templates/api.mustache

@@ -29,6 +29,8 @@ type {{classname}} interface {
 @param ctx context.Context - for authentication, logging, cancellation, deadlines, tracing, etc. Passed from http.Request or context.Background().{{#pathParams}}
 @param {{paramName}}{{#description}} {{{.}}}{{/description}}{{/pathParams}}
 @return {{#structPrefix}}{{&classname}}{{/structPrefix}}{{^structPrefix}}Api{{/structPrefix}}{{operationId}}Request
+
+// Deprecated: Will be removed after 2026-09-30. Move to the packages generated for each available API version instead
 	*/
 	{{{nickname}}}(ctx context.Context{{#pathParams}}, {{paramName}} {{{dataType}}}{{/pathParams}}) {{#structPrefix}}{{&classname}}{{/structPrefix}}{{^structPrefix}}Api{{/structPrefix}}{{operationId}}Request
 	/*
@@ -56,6 +58,7 @@ type {{#structPrefix}}{{&classname}}{{/structPrefix}}{{^structPrefix}}Api{{/stru
 {{vendorExtensions.x-export-param-name}}({{paramName}} {{{dataType}}}) {{#structPrefix}}{{&classname}}{{/structPrefix}}{{^structPrefix}}Api{{/structPrefix}}{{operationId}}Request
 {{/isPathParam}}
 {{/allParams}}
+    // Deprecated: Will be removed after 2026-09-30. Move to the packages generated for each available API version instead
     Execute() ({{#returnType}}{{^isArray}}{{^returnTypeIsPrimitive}}{{^isResponseFile}}*{{/isResponseFile}}{{/returnTypeIsPrimitive}}{{/isArray}}{{{.}}}, {{/returnType}} error)
 }