Update Dockerfile.blueapi to always use latest blueapi image

[DominicOram]

To make sure we are always up-to-date it would be better to use FROM ghcr.io/diamondlightsource/blueapi:latest rather than pinning to a specific version.

At the moment we have to pin to an older version because:

• The blueAPI base image switches to USER ubuntu at the end and so we do not have apt install permissions. To fix this we need to move to USER root then back
• When we do this we see an error of:

 #6 [3/4] RUN /venv/bin/pip install --no-cache-dir --no-compile mx-bluesky
#6 0.052 /bin/sh: 1: /venv/bin/pip: not found
#6 ERROR: process "/bin/sh -c /venv/bin/pip install --no-cache-dir --no-compile mx-bluesky" did not complete successfully: exit code: 127
------
 > [3/4] RUN /venv/bin/pip install --no-cache-dir --no-compile mx-bluesky:
0.052 /bin/sh: 1: /venv/bin/pip: not found
------
Dockerfile.blueapi:16
--------------------
  14 |         apt install -y libgl1 libglib2.0-0
  15 |     
  16 | >>> RUN /venv/bin/pip install --no-cache-dir --no-compile mx-bluesky
  17 |     
  18 |     # Needed so that Blueapi's setup-scratch stage has permission to modify dependencies installed 
--------------------
ERROR: failed to build: failed to solve: process "/bin/sh -c /venv/bin/pip install --no-cache-dir --no-compile mx-bluesky" did not complete successfully: exit code: 127

I think this might be because BlueAPI is now using uv rather than pip. If we update to the latest copier template we will also be using uv so maybe we need to do that first

Acceptance Criteria

• Our container build uses blueapi:latest and works