Consolidate reviewers and assignees in templates

.gitlab/issue_templates/*:
Remove pierre from list of main keys.

.gitlab/merge_request_templates/*:
Use group of main key holders when assigning reviewers, instead of
listing them all separately.

.gitlab/issue_templates/New Packager Key.md

@@ -69,7 +69,6 @@ the details section.
   - [ ] @demize
   - [ ] @diabonas
   - [ ] @dvzrv
-  - [ ] @pierre
 
 ### Developers of the archlinux-keyring project
 - [ ] The data in the [Details](#details) section is correct and signed with a

.gitlab/issue_templates/Remove Packager Key.md

@@ -41,4 +41,3 @@ merge request to this repository using `keyringctl`.
 - [ ] @demize
 - [ ] @diabonas
 - [ ] @dvzrv
-- [ ] @pierre

.gitlab/merge_request_templates/New Main Key.md

@@ -5,7 +5,7 @@ It is used by users with a valid packager key after all steps in an
 accompanying issue (opened with the template "New Main Key") have been
 fulfilled.
 -->
-/assign_reviewer @allan @anthraxx @bluewind @diabonas @dvzrv @pierre
+/assign @archlinux/teams/main-key-holders
 /label ~"new main key"
 /title Add main key of <!-- MODIFY: Add the main key holder's username -->
 <!--

.gitlab/merge_request_templates/New Packager Key.md

@@ -5,7 +5,7 @@ It is either used by the sponsor of a new packager or by an existing packager
 when adding a new key for themself after all steps in an accompanying issue
 (opened with the template "New Packager Key") have been fulfilled..
 -->
-/assign_reviewer @allan @anthraxx @bluewind @diabonas @dvzrv @pierre
+/assign_reviewer @archlinux/teams/main-key-holders
 /label ~"new packager key"
 /title Add packager key of <!-- MODIFY: Add the packager key holder's username -->
 <!--

.gitlab/merge_request_templates/Remove Main Key.md

@@ -4,7 +4,7 @@ from the distribution's keyring.
 It is used by users with a valid main key after all steps in an accompanying
 issue (opened with the template "Remove Main Key") have been fulfilled.
 -->
-/assign_reviewer @allan @anthraxx @bluewind @diabonas @dvzrv @pierre
+/assign_reviewer @archlinux/teams/main-key-holders
 /label ~"remove main key"
 /title Remove main key of <!-- MODIFY: Add the main key holder's username -->
 <!--

.gitlab/merge_request_templates/Remove Packager Key.md

@@ -5,7 +5,7 @@ It is used by users with a valid main key or a valid packager key after all
 steps in an accompanying issue (opened with the template "Remove Packager Key")
 have been fulfilled.
 -->
-/assign_reviewer @allan @anthraxx @bluewind @diabonas @dvzrv @pierre
+/assign_reviewer @archlinux/teams/main-key-holders
 /label ~"remove packager key"
 /title Remove packager key of <!-- MODIFY: Add the packager's username -->
 <!--