feat(docker): add custom image and tag env configuration (#306)

- Replace hardcoded image values with overrideable env variables
- Standardize version env var from LVA_VERSION to LVA_IMAGE_TAG
- Add new env options documentation to .env.example
- Add dev.env to gitignore
- Disable default mic noise suppression in dev compose

BREAKING CHANGE: LVA_VERSION env var replaced with LVA_IMAGE_TAG

.env.example

@@ -1,6 +1,10 @@
 # Linux-Voice-Assistant - Docker Environment Configuration
 # Copy this file to .env and customize for your setup by 'cp .env.example .env'
 
+### Specify another docker image (optional):
+# LVA_IMAGE="ghcr.io/ohf-voice/linux-voice-assistant"
+# LVA_IMAGE_TAG="latest"
+
 ### Enable debug mode (optional):
 # ENABLE_DEBUG="1"
 
@@ -76,6 +80,3 @@ LVA_PULSE_COOKIE="/run/user/${LVA_USER_ID}/pulse/cookie"
 
 ### Enable output-only mode (optional):
 # ENABLE_OUTPUT_ONLY="1"
-
-### Optionally specify a docker tag other than "latest"
-# LVA_VERSION=nightly