ci, build: update CI, libraries, python dependencies, and format

[DnPlas]

This commit updates the CI with standard CI configuration (juju, actions, deps) that is shared across multiple repositories. All python dependencies are also updated to their latest working versions. This PR also includes library updates. Finally, some formatting was applied on non-compliant files (copyright, style).

This change also contains a fix for #84, an issue caused by a missing toolchain in the charm that allows building certain python packages. For more information, please refer to canonical/bundle-kubeflow#648.

Fixes #84
Part of canonical/bundle-kubeflow#648

[phoevos]

Please don't forget the following:

diff --git a/charms/tensorboard-controller/requirements-lint.in b/charms/tensorboard-controller/requirements-lint.in
index c77cd87..07a4a51 100644
--- a/charms/tensorboard-controller/requirements-lint.in
+++ b/charms/tensorboard-controller/requirements-lint.in
@@ -1,9 +1,8 @@
+black
 codespell
-flake8<6
+flake8
 flake8-builtins
-# Pinned because `flake8-copyright==0.2.3` is incompatible with `flake8>=6`.  Can unpin this
-# when https://github.com/savoirfairelinux/flake8-copyright/pull/20 or a similar fix is released
 flake8-copyright
+isort
 pep8-naming
 pyproject-flake8
--r requirements-fmt.txt
diff --git a/requirements-integration.in b/requirements-integration.in
index a07d242..e1a657e 100644
--- a/requirements-integration.in
+++ b/requirements-integration.in
@@ -1,4 +1,6 @@
 # Pinning to <3.0 to ensure compatibility with the 2.9 controller version
 # Note: 3.0 is not being maintained anymore
 juju<3.0
+pytest
 pytest-operator
+pyyaml