chore: move to Eslint flat config

Make the big move to Eslint flat config format. The outcome of Eslint
still should be the same, but some things has changed:
- `eslint-plugin-github` is dropped, flat configs have been out for a
while and most eslint plugins support it, but for no reason and no
activity in sight this plugin is likely not going to support flat config
for a while and to avoid other plugins not being able to update (as they
are requiring flat configs) drop the github rules.
- Nested configs don't work properly and are unified into the root
eslint config, this unification did cause some conflicts and thats why
the `import-x` is in a seperate 'group' to exclude targeting Vue files.
- The `eslint-plugin-i` is deprecated and `esplint-plugin-import-x` is
its succesor which has better support for flat configs, the same rules
are still applied.

The majority of the flat config was generated by
`@eslint/migrate-config` tool.

Makefile

@@ -164,7 +164,7 @@ TAR_EXCLUDES := .git data indexers queues log node_modules $(EXECUTABLE) $(FOMAN
 GO_DIRS := build cmd models modules routers services tests
 WEB_DIRS := web_src/js web_src/css
 
-ESLINT_FILES := web_src/js tools *.js tests/e2e/*.js tests/e2e/shared/*.js
+ESLINT_FILES := web_src/js tools *.js *.mjs tests/e2e/*.js tests/e2e/shared/*.js
 STYLELINT_FILES := web_src/css web_src/js/components/*.vue
 SPELLCHECK_FILES := $(GO_DIRS) $(WEB_DIRS) docs/content templates options/locale/locale_en-US.ini .github $(wildcard *.go *.js *.md *.yml *.yaml *.toml)
 
@@ -437,11 +437,11 @@ lint-codespell-fix-i:
 
 .PHONY: lint-js
 lint-js: node_modules
-	npx eslint --color --max-warnings=0 --ext js,vue $(ESLINT_FILES)
+	npx eslint --color --max-warnings=0 $(ESLINT_FILES)
 
 .PHONY: lint-js-fix
 lint-js-fix: node_modules
-	npx eslint --color --max-warnings=0 --ext js,vue $(ESLINT_FILES) --fix
+	npx eslint --color --max-warnings=0 $(ESLINT_FILES) --fix
 
 .PHONY: lint-css
 lint-css: node_modules