TF-3336 Make Echo ping of web socket optional

[tddang-linagora]

Issue

• Websocket PING (important) #3336

Demo

Screen.Recording.2024-12-17.at.10.47.24.mov

[github-actions]

This PR has been deployed to https://linagora.github.io/tmail-flutter/3355.

[chibenwa]

Misses documentation on how to turn this on and off and default value.

I am a flutter outsider.

If you wish me to do that for you please document it!

[tddang-linagora]

Misses documentation on how to turn this on and off and default value.

I am a flutter outsider.

If you wish me to do that for you please document it!

In case you missed the adr no. 56 of this PR

- Echo ping will still be left as an option in `env.file` through `WS_ECHO_PING`
  - Set it to `true` if you want to use Echo ping
  - Set it to `false` or left it as is if you don't want to use Echo ping

[dab246]

• Add WS_ECHO_PING in env.file

[dab246]

• Please attach demo video to verify it still work well.

[hoangdat]

I tested in mail.lin-saas.dev, to keep it all night. Still work well.

[dab246]

LGTM

The base branch was changed.