[FEAT] Custom login screen icon + custom app name (#1500)

* implement custom icon on login screen for single & multi user + custom app name feature

* hide field when not relevant

* set customApp name

* show original anythingllm login logo unless custom logo is set

* nit-picks

* remove console log

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Co-authored-by: timothycarambat <rambat1010@gmail.com>