Remove need for 'ISPYB_CREDENTIALS' environment variable

[tieneupin]

Resolves issue #587 .

ispyb.sqlalchemy.url() takes credentials as an argument, through which the config file can be passed directly to the function instead of relying on the ISPYB_CREDENTIALS environment variable. This eliminates the last traces of our repo's need to explicitly define ISPYB_CREDENTIALS.

Additionally, elements of the CI workflow and test code related to the Murfey and ISPyB databases have also been modified. ISPYB_CREDENTIALS has also been dropped successfully from the test workflow, and fixtures have been put in place to allow for the creation of databases that will be reset to a desired initial state at the end of every test. This means that the database does not have to be shut down and rebooted with every database-related test, which should help with our testing times as we continue to improve Murfey's test coverage.

NOTE: Within our code base, it looks like ISPyB spawns SQLAlchemy Session objects, whereas the Murfey database spawns SQLModel ones. As such, SQLModel's functions might not work when querying the ISPyB database. The database session fixtures for the ISPyB and Murfey test databases have been written to reflect this.

[codecov]

Codecov Report

Attention: Patch coverage is 31.25000% with 22 lines in your changes missing coverage. Please review.

Project coverage is 30.17%. Comparing base (88a6f93) to head (f0f70f3).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #588      +/-   ##
==========================================
+ Coverage   30.15%   30.17%   +0.01%     
==========================================
  Files          80       80              
  Lines       10514    10517       +3     
  Branches     1405     1406       +1     
==========================================
+ Hits         3171     3174       +3     
+ Misses       7238     7237       -1     
- Partials      105      106       +1     

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