Install BATS (Bash Automated Testing System) in sonic-mgmt docker. (#22137)

Why I did it
Use for unit testing bash scripts.

Work item tracking
Microsoft ADO (number only): 31736455

How I did it
Add installation at the Dockerfile

How to verify it
build sonic-mgmt docker
make -f Makefile.work BLDENV=bullseye SONIC_BUILD_JOBS=$(nproc) DEFAULT_CONTAINER_REGISTRY=publicmirror.azurecr.io ENABLE_DOCKER_BASE_PULL=y LEGACY_SONIC_MGMT_DOCKER=n target/docker-sonic-mgmt.gz
load it:
docker load -i target/docker-sonic-mgmt.gz
f2a185d061e0: Loading layer [==================================================>]  3.267GB/3.267GB
Loaded image: docker-sonic-mgmt:latest
run bats --version
docker run --rm docker-sonic-mgmt:latest bats --version

Bats 1.11.1

Author: hdwhdw

dockers/docker-sonic-mgmt/Dockerfile.j2

@@ -39,7 +39,8 @@ RUN apt-get update && apt-get install -y apt-transport-https \
                                          sudo \
                                          tcpdump \
                                          telnet \
-                                         vim
+                                         vim \
+                                         bats
 
 RUN python3 -m pip install --upgrade pip setuptools wheel
 RUN python3 -m pip install aiohttp \