docs: Document all environment variable usage in PyFluent #10722

Job	Run time
Code style	1m 19s
Documentation Style Check	14s
Run commit style checks	2s
Build and Smoke tests (ubuntu-latest, 3.10, false)	32s
Build and Smoke tests (ubuntu-latest, 3.11, false)	39s
Build and Smoke tests (ubuntu-latest, 3.12, false)	35s
Build and Smoke tests (ubuntu-latest, 3.13, false)	50s
Build and Smoke tests (windows-latest, 3.10, false)	1m 46s
Build and Smoke tests (windows-latest, 3.11, false)	3m 1s
Build and Smoke tests (windows-latest, 3.12, false)	2m 14s
Build and Smoke tests (windows-latest, 3.13, false)	3m 22s
Build Documentation	3m 1s
Build	23m 8s
Unit Testing (v22.2.0, 222)	6m 15s
Unit Testing (v23.1.0, 231)	7m 52s
Unit Testing (v23.2.0, 232)	12m 35s
Unit Testing (v24.1.0, 241)	12m 48s
Unit Testing (v24.2.0, 242)	19m 59s
Unit Testing (v25.1.0, 251)	20m 3s
Release	0s
	2h 0m 15s

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