[FEAT REQ] `opacity` prop

[gabrieljablonski]

Is your feature request related to a problem? Please describe.
Previously, the way to change the tooltip opacity (from the 0.9 default value) was to set the CSS variable like so:

:root {
  --rt-opacity: 1;
}

I believe the recent change in the way the styles are injected broke this.

Describe the solution you'd like

• Add a opacity tooltip prop to override the default value.
• Add a check on the style prop and console.warn() if opacity is set (only if env !== 'production'), advising to use the prop instead (same as done with border).

Additional context
As mentioned on #1010 (comment).

[danielbarion]

I didn't realize the CSS tokens override is no longer working after the CSS injection feature, but this makes sense! Nice catch!

This gave me one idea: #1052

Please feel free to continue the implementation

[gabrieljablonski]

Available with react-tooltip@5.18.0.