Replace python-ldap with openldap in conda env

On PyPI, `python-ldap` is distributed as an *sdist* only, not *wheel*.
But it still requires a compilation step before installation.

Some dependencies installed with conda are rightfully ignored by Poetry.
Even when `python-ldap` is pre-installed by conda,
Poetry would still need to reinstall it which implies compilation.
Indeed there is an issue in how conda packages are created
and how they are installed:
* <python-poetry/poetry#6408 (comment)>
* <conda-forge/python-ldap-feedstock#28>

So it does not make much sense to let conda install `python-ldap`.
Instead we can instruct conda to install `openldap` only,
and pip and Poetry should be able to compile `python-ldap`.

GitHub: mxcube#1510
GitHub: mxcube/mxcubecore#849 (comment)
GitHub: conda-forge/python-ldap-feedstock#28
GitHub: mxcube/mxcubecore#851

conda-environment.yml

@@ -1,24 +1,28 @@
 ---
+
 name: mxcubeweb
 
 channels:
   - conda-forge
 
 dependencies:
-  # ====================
+
   # Runtime dependencies
   # ====================
 
   - ffmpeg  # Not directly used by mxcube, but necessary for the video-streamer
   - python >=3.8,<3.12  # Make sure it matches `pyproject.toml`
 
-  # We install `python-ldap` from conda because it is "hard" to install.
-  # On PyPI it is not available as *wheel*, only as *sdist* which requires to be built
-  # with compilation steps that require a compiler and some header files.
-  # Installing with conda is much "easier".
-  - python-ldap ==3.4.3  # Make sure it matches `poetry.lock`
 
-  # ========================
+  # Compile-time dependencies
+  # =========================
+
+  # Adding `openldap` here allows Python's pip and Poetry to compile `python-ldap`.
+  # Indeed on PyPI, `python-ldap` is distributed as *sdist* only
+  # and it requires compilation before it can be installed.
+  - openldap
+
+
   # Development dependencies
   # ========================