doc: review: switch labels to a definition list

Move labels docs from headers to a definition list.

Signed-off-by: Anas Nashif <anas.nashif@intel.com>

doc/project/dev_env_and_tools.rst

@@ -65,8 +65,6 @@ Categories/Labels
 -----------------
 
 Hotfix
-++++++
-
   Any change that is a fix to an issue that blocks developers from doing their
   daily work, for example CI breakage, Test breakage, Minor documentation fixes
   that impact the user experience.
@@ -77,8 +75,6 @@ author) they can be merged with justification without review by one of the
   project owners.
 
 Trivial
-+++++++
-
   Trivial changes are those that appear obvious enough and do not require maintainer or code-owner
   involvement. Such changes should not change the logic or the design of a
   subsystem or component. For example a trivial change can be:
@@ -91,8 +87,6 @@ subsystem or component. For example a trivial change can be:
   - Sample modifications to support additional configuration or boards etc.
 
 Maintainer
-+++++++++++
-
   Any changes that touch the logic or the original design of a subsystem or
   component will need to be reviewed by the code owner or the designated subsystem
   maintainer. If the code changes is initiated by a contributor or developer other
@@ -101,14 +95,10 @@ have to drive the pull request to a mergeable state by giving feedback to the
   author and asking for more reviews from other developers.
 
 Security
-+++++++++++
-
   Changes that appear to have an impact to the overall security of the system need
   to be reviewed by a security expert from the security working group.
 
 TSC and Working Groups
-++++++++++++++++++++++
-
   Changes that introduce new features or functionality or change the way the
   overall system works need to be reviewed by the TSC or the responsible Working
   Group. For example for :ref:`breaking API changes <breaking_api_changes>`, the