Adding upstream version 5.2.3+dfsg.

Signed-off-by: Daniel Baumann <daniel@debian.org>

.github/ISSUE_TEMPLATE/bug_report.yml

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+name: Report a bug
+description: Tell us about a bug or issue you may have identified in Bootstrap.
+title: "Provide a general summary of the issue"
+labels: [bug]
+assignees: "-"
+body:
+  - type: checkboxes
+    attributes:
+      label: Prerequisites
+      description: Take a couple minutes to help our maintainers work faster.
+      options:
+        - label: I have [searched](https://github.com/twbs/bootstrap/issues?utf8=%E2%9C%93&q=is%3Aissue) for duplicate or closed issues
+          required: true
+        - label: I have [validated](https://html5.validator.nu/) any HTML to avoid common problems
+          required: true
+        - label: I have read the [contributing guidelines](https://github.com/twbs/bootstrap/blob/main/.github/CONTRIBUTING.md)
+          required: true
+  - type: textarea
+    id: what-happened
+    attributes:
+      label: Describe the issue
+      description: Provide a summary of the issue and what you expected to happen, including specific steps to reproduce.
+    validations:
+      required: true
+  - type: textarea
+    id: reduced-test-case
+    attributes:
+      label: Reduced test cases
+      description: Include links [reduced test case](https://css-tricks.com/reduced-test-cases/) links or suggested fixes using CodePen ([v4 template](https://codepen.io/team/bootstrap/pen/yLabNQL) or [v5 template](https://codepen.io/team/bootstrap/pen/qBamdLj)).
+    validations:
+      required: true
+  - type: dropdown
+    id: os
+    attributes:
+      label: What operating system(s) are you seeing the problem on?
+      multiple: true
+      options:
+        - Windows
+        - macOS
+        - Android
+        - iOS
+        - Linux
+    validations:
+      required: true
+  - type: dropdown
+    id: browser
+    attributes:
+      label: What browser(s) are you seeing the problem on?
+      multiple: true
+      options:
+        - Chrome
+        - Safari
+        - Firefox
+        - Microsoft Edge
+        - Opera
+  - type: input
+    id: version
+    attributes:
+      label: What version of Bootstrap are you using?
+      placeholder: "e.g., v5.1.0 or v4.5.2"
+    validations:
+      required: true

.github/ISSUE_TEMPLATE/config.yml

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+contact_links:
+  - name: Ask the community
+    url: https://github.com/twbs/bootstrap/discussions/new
+    about: Ask and discuss questions with other Bootstrap community members.

.github/ISSUE_TEMPLATE/feature_request.yml

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+name: Feature request
+description: Suggest new or updated features to include in Bootstrap.
+title: "Suggest a new feature"
+labels: [feature]
+assignees: []
+body:
+  - type: checkboxes
+    attributes:
+      label: Prerequisites
+      description: Take a couple minutes to help our maintainers work faster.
+      options:
+        - label: I have [searched](https://github.com/twbs/bootstrap/issues?utf8=%E2%9C%93&q=is%3Aissue) for duplicate or closed feature requests
+          required: true
+        - label: I have read the [contributing guidelines](https://github.com/twbs/bootstrap/blob/main/.github/CONTRIBUTING.md)
+          required: true
+  - type: textarea
+    id: proposal
+    attributes:
+      label: Proposal
+      description: Provide detailed information for what we should add, including relevant links to prior art, screenshots, or live demos whenever possible.
+    validations:
+      required: true
+  - type: textarea
+    id: motivation
+    attributes:
+      label: Motivation and context
+      description: Tell us why this change is needed or helpful, and what problems it may help solve.
+    validations:
+      required: true