replace travis CI with github actions (check syntax, check links)

- travis CI free plans were discontinued
- CI pipeline is similar to https://github.com/awesome-selfhosted/awesome-selfhosted-data and uses https://github.com/nodiscc/hecat
- the pipeline will not pass until https://github.com/awesome-foss/awesome-sysadmin/issues/416 has been fixed
- ref. https://github.com/awesome-foss/awesome-sysadmin/issues/405

.hecat/awesome-lint.yml

@@ -0,0 +1,8 @@
+steps:
+  - name: check data against awesome-sysadmin guidelines
+    module: processors/awesome_lint
+    module_options:
+      source_directory: ./
+      licenses_files:
+        - licenses.yml
+        - licenses-nonfree.yml

.hecat/import.yml

@@ -0,0 +1,6 @@
+steps:
+  - name: import awesome-sysadmin README.md to YAML
+    module: importers/markdown_awesome
+    module_options:
+      source_file: ./README.md
+      output_directory: ./

.hecat/url-check.yml

@@ -0,0 +1,11 @@
+steps:
+  - name: check URLs
+    module: processors/url_check
+    module_options:
+      source_directories:
+        - software
+        - tags
+      source_files:
+        - licenses.yml
+      errors_are_fatal: True
+      exclude_regex: []