feat: Add "decimals" per entity & "decimals_secondary" options

[ildar170975]

A detailed description taken from an updated Readme:
Options decimals defined "card-wide" and/or for some entity are used to set an exact number of decimals according to the following rules:

1. For states:
   -- if none decimals option is defined - a default presentation is used;
   -- if "card-wide" decimals is defined - this value is used;
   -- if decimals for some entity is defined - this value is used for this entity.

2. For extrema & average values:
   -- if none decimals option is defined - a default presentation is used;
   -- if "card-wide" decimals is defined - this value is used;
   -- if decimals is defined for the 1st entity - this value is used.

3. For primary Y-axis labels:
   -- if "card-wide" decimals option is not defined - a default presentation is used;
   -- otherwise - this value is used.

4. For secondary Y-axis labels:
   -- if "card-wide" decimals & decimals_secondary option are not defined - a default presentation is used;
   -- if "card-wide" decimals option is defined - this value is used;
   -- if "card-wide" decimals_secondary option is defined - this value is used.

Here a "default presentation" will be (under construction) based on a precision settings provided in entity settings, selected language & global number format.

[ildar170975]

Implements #863

[zagi988]

Will this be ever added?
It's a very useful feature, please add it.

[ildar170975]

It will be added along with a forthcoming feature to show states according to their own settings (number format, precision).