allow setting the session pool size in niquests

[sjoeboo]

Description

adds ability to set the session pool size in niquests when needed:

grafana = GrafanaApi.from_url(
    url=GRAFANA_URL, credential=TokenAuth(token=GRAFANA_API_TOKEN)
)
grafana.client.timeout = 60
grafana.client.session_pool_size = 32

Checklist

• The patch has appropriate test coverage
• The patch follows the style guidelines of this project
• The patch has appropriate comments, particularly in hard-to-understand areas
• The documentation was updated corresponding to the patch
• I have performed a self-review of this patch

[sjoeboo]

addresses #189

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 92.29%. Comparing base (7303ec2) to head (dcca2ae).
Report is 48 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #190      +/-   ##
==========================================
- Coverage   94.44%   92.29%   -2.16%     
==========================================
  Files          26       27       +1     
  Lines        1711     1816     +105     
==========================================
+ Hits         1616     1676      +60     
- Misses         95      140      +45     

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[amotl]

Thanks!