[DPE-4614] Add support for tracing through tempo-k8s (#149)

## Issue
We would like to be able to instrument our charm and generate traces to
discover inefficiencies in charm code execution. The observability team
has developed a charm for
[tempo](https://github.com/canonical/tempo-k8s-operator) that we would
like to integrate with.

## Solution
Integrate with the tempo charm

## Considerations
1. We are not supporting sending traces to tempo-k8s using HTTPS are
there are still some rough edges to be rounded with this integration
2. We need to use the `edge` version of cos-lite until they release to
stable as it contains some critical fixes


![image](https://github.com/canonical/mysql-router-operator/assets/99665202/f4bd2bce-0b7f-4e1c-9794-129ba5f84cb4)

.github/workflows/ci.yaml

@@ -108,11 +108,11 @@ jobs:
             bases-index: 0
           - series: jammy
             bases-index: 1
-        juju-snap-channel:  ["2.9/stable", "3.1/stable"]
+        juju-snap-channel:  ["2.9/stable", "3.4/stable"]
         include:
-          - juju-snap-channel: "3.1/stable"
-            agent-version: "3.1.6"
-            libjuju-version:  "3.2.2"
+          - juju-snap-channel: "3.4/stable"
+            agent-version: "3.4.3"
+            libjuju-version:  "3.4.0.0"
           - juju-snap-channel: "2.9/stable"
             agent-version: "2.9.45"
             libjuju-version:  "2.9.44.1"

lib/charms/data_platform_libs/v0/data_interfaces.py

@@ -331,7 +331,7 @@ def _on_topic_requested(self, event: TopicRequestedEvent):
 
 # Increment this PATCH version before using `charmcraft publish-lib` or reset
 # to 0 if you are raising the major API version
-LIBPATCH = 35
+LIBPATCH = 37
 
 PYDEPS = ["ops>=2.0.0"]
 
@@ -642,22 +642,26 @@ def _move_to_new_label_if_needed(self):
             return
 
         # Create a new secret with the new label
-        old_meta = self._secret_meta
         content = self._secret_meta.get_content()
+        self._secret_uri = None
 
         # I wish we could just check if we are the owners of the secret...
         try:
             self._secret_meta = self.add_secret(content, label=self.label)
         except ModelError as err:
             if "this unit is not the leader" not in str(err):
                 raise
-        old_meta.remove_all_revisions()
+        self.current_label = None
 
     def set_content(self, content: Dict[str, str]) -> None:
         """Setting cached secret content."""
         if not self.meta:
             return
 
+        # DPE-4182: do not create new revision if the content stay the same
+        if content == self.get_content():
+            return
+
         if content:
             self._move_to_new_label_if_needed()
             self.meta.set_content(content)
@@ -1586,7 +1590,7 @@ def _register_secret_to_relation(
         """
         label = self._generate_secret_label(relation_name, relation_id, group)
 
-        # Fetchin the Secret's meta information ensuring that it's locally getting registered with
+        # Fetching the Secret's meta information ensuring that it's locally getting registered with
         CachedSecret(self._model, self.component, label, secret_id).meta
 
     def _register_secrets_to_relation(self, relation: Relation, params_name_list: List[str]):
@@ -2309,7 +2313,7 @@ def _secrets(self) -> dict:
         return self._cached_secrets
 
     def _get_secret(self, group) -> Optional[Dict[str, str]]:
-        """Retrieveing secrets."""
+        """Retrieving secrets."""
         if not self.app:
             return
         if not self._secrets.get(group):

lib/charms/operator_libs_linux/v2/snap.py

@@ -83,7 +83,7 @@
 
 # Increment this PATCH version before using `charmcraft publish-lib` or reset
 # to 0 if you are raising the major API version
-LIBPATCH = 5
+LIBPATCH = 7
 
 
 # Regex to locate 7-bit C1 ANSI sequences
@@ -319,7 +319,10 @@ def get(self, key: Optional[str], *, typed: bool = False) -> Any:
                 Default is to return a string.
         """
         if typed:
-            config = json.loads(self._snap("get", ["-d", key]))
+            args = ["-d"]
+            if key:
+                args.append(key)
+            config = json.loads(self._snap("get", args))
             if key:
                 return config.get(key)
             return config
@@ -584,13 +587,16 @@ def ensure(
                     "Installing snap %s, revision %s, tracking %s", self._name, revision, channel
                 )
                 self._install(channel, cohort, revision)
-            else:
+                logger.info("The snap installation completed successfully")
+            elif revision is None or revision != self._revision:
                 # The snap is installed, but we are changing it (e.g., switching channels).
                 logger.info(
                     "Refreshing snap %s, revision %s, tracking %s", self._name, revision, channel
                 )
                 self._refresh(channel=channel, cohort=cohort, revision=revision, devmode=devmode)
-            logger.info("The snap installation completed successfully")
+                logger.info("The snap refresh completed successfully")
+            else:
+                logger.info("Refresh of snap %s was unnecessary", self._name)
 
         self._update_snap_apps()
         self._state = state