Update env-configuration.md

[silentoplayz]

Update Open WebUI's list of environment variables (v0.3.20 -> v0.5.11). My apologies for the two separate initial commits rather than one to help compare side-by-side. I'm still learning GitHub Desktop.

This PR adds environment variables accessed by Open WebUI, but were not previously documented. I also tried to sort the environment variables the best I could, so there's a bunch of new categories.

Future improvements to Open WebUI's list of environment variables can include:

• Distinguishing between persistent and non-persistent environment variables.
• Listing available options (Sorta Hard) and default values (should mostly be complete) for restricted environment variables where necessary.
• Identifying incompatible variable combinations and provide warnings or notes. (Hard)
• Reviewing each environment variable and fixing any misinformation to improve correctness. (Also Hard)

Before:

After:

[0xThresh]

Thank you for such a great effort on getting the docs updated!

[silentoplayz]

Is this ready to be merged? In the future, I believe the env list page could be updated if necessary. This already is a huge bump to the details on the page.