ci: modernize GitHub workflows and templates

Update CI workflow: restrict triggers to master+PRs, add concurrency
groups and npm cache. Update release-please and stale workflows to
latest action versions. Replace single ISSUE_TEMPLATE.md with YAML-
based templates (bug report, feature request, config). Rewrite
CONTRIBUTING.md for awesome-cordova-plugins.

.github/ISSUE_TEMPLATE/bug_report.yml

@@ -0,0 +1,63 @@
+name: Bug Report
+description: Report a bug in an Awesome Cordova Plugins wrapper
+labels: ["bug"]
+body:
+  - type: markdown
+    attributes:
+      value: |
+        Thanks for taking the time to report a bug! Please fill out the sections below.
+
+  - type: input
+    id: plugin
+    attributes:
+      label: Plugin
+      description: Which @awesome-cordova-plugins/* package is affected?
+      placeholder: e.g. @awesome-cordova-plugins/camera
+    validations:
+      required: true
+
+  - type: textarea
+    id: current-behavior
+    attributes:
+      label: Current behavior
+      description: Describe what happens.
+    validations:
+      required: true
+
+  - type: textarea
+    id: expected-behavior
+    attributes:
+      label: Expected behavior
+      description: Describe what you expected to happen.
+    validations:
+      required: true
+
+  - type: textarea
+    id: steps
+    attributes:
+      label: Steps to reproduce
+      description: How can we reproduce the issue?
+    validations:
+      required: true
+
+  - type: textarea
+    id: environment
+    attributes:
+      label: Environment
+      description: |
+        Relevant versions (fill in what you can):
+      value: |
+        - @awesome-cordova-plugins/core version:
+        - Cordova / Capacitor version:
+        - Angular version:
+        - Platform (iOS / Android / Browser):
+    validations:
+      required: false
+
+  - type: textarea
+    id: additional
+    attributes:
+      label: Additional context
+      description: Any other information, stack traces, or screenshots.
+    validations:
+      required: false

.github/ISSUE_TEMPLATE/config.yml

@@ -0,0 +1,5 @@
+blank_issues_enabled: false
+contact_links:
+  - name: Support & Questions
+    url: https://github.com/danielsogl/awesome-cordova-plugins/discussions
+    about: Please use Discussions for support requests and questions.

.github/ISSUE_TEMPLATE/feature_request.yml

@@ -0,0 +1,35 @@
+name: Feature Request
+description: Suggest a new plugin wrapper or enhancement
+labels: ["enhancement"]
+body:
+  - type: markdown
+    attributes:
+      value: |
+        Have a plugin you'd like to see supported? Since Awesome Cordova Plugins
+        is a set of wrappers for Cordova plugins, adding support is as easy as
+        creating a new wrapper.
+
+  - type: textarea
+    id: description
+    attributes:
+      label: Description
+      description: What plugin or feature would you like to see added or improved?
+    validations:
+      required: true
+
+  - type: input
+    id: plugin-repo
+    attributes:
+      label: Cordova plugin repository
+      description: Link to the Cordova plugin (if requesting a new wrapper).
+      placeholder: https://github.com/example/cordova-plugin-example
+    validations:
+      required: false
+
+  - type: textarea
+    id: use-case
+    attributes:
+      label: Use case
+      description: Describe why this would be useful.
+    validations:
+      required: false