Enable websocket feature by default

[swanandx]

This PR does following:

• enable websocket feature by default
• remove old "websockets" feature
• log warning if ws config is getting ignored

Type of change

• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist:

• Formatted with cargo fmt
• Make an entry to CHANGELOG.md if it's relevant to the users of the library. If it's not relevant mention why.

[h3nill]

changes LGTM, but i rememver last time having a feature with same name between rumqttc and rumqttd caused some problem. Can you check if its still the case?

more context here: #633

[swanandx]

I ran cargo r --bin rumqttd --features websocket from root of repo and it works without any issues!

IIRC, the issue was it enabled websocket feature for both rumqttc and rumqttd and some dependencies caused conflicts.and to specify depency for a single package, you suggested this.

PS: tested cargo r --bin rumqttd as well to verify it is enabled by default.