Add theme text color config options (streamlit#12438)

Add configurable text colors for theming:
- `redTextColor`
- `orangeTextColor`
- `yellowTextColor`
- `blueTextColor`
- `greenTextColor`
- `violetTextColor`
- `grayTextColor`

**Order of precedence:**
* Uses configured `redTextColor`
* If there is no configured `redTextColor`, derives it from a provided `redColor` (darkened by 15% for light theme and lightened by 15% for dark theme)
* If neither, falls back to default

Author: mayagbarnes

e2e_playwright/__snapshots__/linux/custom_background_colors_test/custom_background_colors_app[chromium].png

@@ -27,6 +27,7 @@
 def configure_custom_theme_background_colors():
     """Configure custom theme background colors."""
     # Also set some main colors for better contrast with background colors
+    # these will trigger derived text colors as well
     os.environ["STREAMLIT_THEME_RED_COLOR"] = "#750000"
     os.environ["STREAMLIT_THEME_GREEN_COLOR"] = "#008000"
     os.environ["STREAMLIT_THEME_GRAY_COLOR"] = "#525252"