feat: authenticate against Tableau on every API call

[fernandobrito]

https://voidev.atlassian.net/browse/DATAPS-1199

From time to time, we started to get connection errors when running this automation internally.

We have changed how we manage the sessions when using the tableauserverclient, and now the issue is gone.

I thought this would have performance implications since we have a loop retrieving details for workbooks, but it barely made a difference.

[codecov-commenter]

Codecov Report

Base: 84.97% // Head: 83.96% // Decreases project coverage by -1.01% ⚠️

Coverage data is based on head (a91fed0) compared to base (b40d7c0).
Patch coverage: 0.00% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #12      +/-   ##
==========================================
- Coverage   84.97%   83.96%   -1.02%     
==========================================
  Files           8        8              
  Lines         233      237       +4     
  Branches       31       36       +5     
==========================================
+ Hits          198      199       +1     
- Misses         27       30       +3     
  Partials        8        8              

Impacted Files	Coverage Δ
src/exposurescrawler/crawlers/tableau.py	89.55% <ø> (-0.16%)	⬇️
src/exposurescrawler/tableau/rest_client.py	45.00% <0.00%> (-10.56%)	⬇️
src/exposurescrawler/dbt/exposure.py	100.00% <0.00%> (ø)
src/exposurescrawler/tableau/models.py	100.00% <0.00%> (ø)
src/exposurescrawler/tableau/graphql_client.py	78.33% <0.00%> (+0.36%)	⬆️

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