Add issue templates for key actions

.gitlab/issue_templates/New Main Key.md:
Add issue template for adding a new main key.

.gitlab/issue_templates/New Packager Key.md:
Add issue template for adding a new packager key.

.gitlab/issue_templates/Remove Main Key.md:
Add issue template for removing a main key.

.gitlab/issue_templates/Remove Packager Key.md:
Add issue template for removing a packager key.

.gitlab/issue_templates/New Main Key.md

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+<!--
+This template is used when a new main PGP public key needs to be added to the
+distribution's keyring.
+It is used by users with a valid packager key.
+-->
+/assign @allan @anthraxx @bluewind @dvzrv @pierre
+/label ~"new main key"
+<!--
+Please do not remove the above quick actions, which automatically label the
+issue and assign relevant users.
+-->
+
+# Add a new main key
+
+## Details
+
+- Username: <!-- Add the @-prefixed username -->
+- PGP key ID: <!-- Add the "long format" key ID of the new PGP public key here -->
+- Revocation Certificate Holder: <!-- Add the @-prefixed username of the revocation certificate holder -->
+
+<!--
+NOTE: Attach the above information as a clearsigned document to this ticket
+using a valid packager key of the user.
+https://www.gnupg.org/gph/en/manual/x135.html
+-->
+
+## Checks
+
+- [ ] The [workflow for adding a new main
+  key](https://gitlab.archlinux.org/archlinux/archlinux-keyring/-/wikis/workflows/add-a-new-main-key)
+  has been followed
+- [ ] The data in the [Details](#details) section is attached to this issue as
+  a clearsigned document
+- [ ] The revocation certificate holder verified the revocation certificate as
+  working in a comment to this issue
+- [ ] The public key has been uploaded to the SKS infrastructure

.gitlab/issue_templates/New Packager Key.md

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+<!--
+This template is used when a new packager PGP public key needs to be added to
+the distribution's keyring.
+It is either used by the sponsor of a new packager or by an existing packager
+when adding a new key for themself.
+-->
+/assign @allan @anthraxx @bluewind @dvzrv @pierre
+/label ~"new packager key"
+<!--
+Please do not remove the above quick actions, which automatically label the
+issue and assign relevant users.
+-->
+
+# Add a new packager key
+
+## Details
+
+- Username: <!-- Add the @-prefixed username -->
+- PGP key ID: <!-- Add the "long format" key ID of the new PGP public key here -->
+- Sponsors: <!-- Add the @-prefixed usernames of the sponsors -->
+- Application: <!-- Add link to application, if this is the key of a new packager, else remove -->
+- Results: <!-- Add link to results of application, if this is the key of a new packager, else remove -->
+
+<!--
+NOTE: Attach the above information as a clearsigned document to this ticket.
+https://www.gnupg.org/gph/en/manual/x135.html
+
+If this is the key of a new packager, one of their sponsors needs to do the
+signature.
+If this is a new key of an already existing packager, the packager themself
+needs to do the signature.
+-->
+
+## Checks
+
+- [ ] The [workflow for adding a new packager
+  key](https://gitlab.archlinux.org/archlinux/archlinux-keyring/-/wikis/workflows/add-a-new-packager-key)
+  has been followed
+- [ ] The data in the [Details](#details) section is attached to this issue as
+  a clearsigned document
+- [ ] The public key has been uploaded to the SKS infrastructure
+- [ ] The public key has been signed by at least three valid main keys

.gitlab/issue_templates/Remove Main Key.md

@@ -0,0 +1,26 @@
+<!--
+This template is used when an existing main PGP public key needs to be removed
+from the distribution's keyring.
+It is used by users with a valid main key.
+-->
+/assign @allan @anthraxx @bluewind @dvzrv @pierre
+/label ~"remove main key"
+<!--
+Please do not remove the above quick actions, which automatically label the
+issue and assign relevant users.
+-->
+
+# Remove a main key
+
+## Details
+
+- Username: <!-- Add the @-prefixed username -->
+- PGP key ID: <!-- Add the "long format" key ID of the PGP public key here -->
+- Resignation: <!-- Link to resignation of key holder -->
+
+## Checks
+
+- [ ] There are more than or equal to three valid main keys remaining after
+  removal of this key.
+- [ ] All packagers have at least three valid main key signatures for their
+  packager key after removal of this key.

.gitlab/issue_templates/Remove Packager Key.md

@@ -0,0 +1,24 @@
+<!--
+This template is used when an existing packager PGP public key needs to be
+removed from the distribution's keyring.
+It is used by users with a valid main key or a valid packager key.
+-->
+/assign @allan @anthraxx @bluewind @dvzrv @pierre
+/label ~"remove packager key"
+<!--
+Please do not remove the above quick actions, which automatically label the
+issue and assign relevant users.
+-->
+
+# Remove a packager key
+
+## Details
+
+- Username: <!-- Add the @-prefixed username -->
+- PGP key ID: <!-- Add the "long format" key ID of the PGP public key here -->
+- Resignation: <!-- Link to resignation of key holder -->
+
+## Checks
+
+- [ ] There are no packages left in any of the official repositories, that are
+  signed by the key, that is about to be removed.