1596: Add @typescript-eslint rules and fix issues

[steffenkleinle]

Short description

Add @typescript-eslint rules and fix issues (and add a few eslint-disables).

Proposed changes

• Rewrite .eslintrc to :eslintrc.js
• Use eslint config from integreat-app (and disable a few rules, might be enabled later)
• Enable @tyescript-eslint rules
• Fix most issues

Side effects

None.

Testing

That everything still works?

Resolved issues

Partly fixes: #1596.

[seluianova]

It also fixes this one, right? https://github.com/digitalfabrik/entitlementcard/issues/1296

[steffenkleinle]

Cannot start webpack anymore

Failed to compile.

Invalid configuration object. Webpack has been initialized using a configuration object that does not match the API schema.
 - configuration.resolve.modules[2] should be a non-empty string.
   -> Folder name or directory path where to find modules.

npm ERR! Lifecycle script `start` failed with error: 
npm ERR! Error: command failed 
npm ERR!   in workspace: administration 
npm ERR!   at location: /Users/afischer/projects/entitlementcard/administration 

Process finished with exit code 1

Ohhh... funny, this was caused by this little change:

      modules: ['node_modules', paths.appNodeModules].concat(modules.additionalModulePaths || []),

to

      modules: ['node_modules', paths.appNodeModules].concat(modules.additionalModulePaths ?? []),

Should be fixed now @f1sh1918, can you please test this again? Thanks.