Add float field type for keystone-next

[MurzNN]

I created a float field for Keystone-next, based on code from integer field type with some modifications. Please review it and comment if something done wrong.
If all is done right, I will try to implement double field type via same way.

How to test:

1. In examples-next/basic/schema.ts add the float field type, for example, to "Posts" list:

   Post: list({
     fields: {
       ...
+      float: float(),
        ...
     }
   }),

2. Try to create, update, remove items in "Posts" list - all should work well.

Tested with mongoose and knex adapters.

[changeset-bot]

🦋 Changeset detected

Latest commit: b02dd7b

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@keystone-next/fields	Minor

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[timleslie]

This all looks good to me, thanks for the PR @MurzNN 🙏

@mitchellhamilton Could you please review the Admin UI component and if you're happy with it, give this a ✅ Thanks!

[emmatown]

This logic should be identical to the logic in integer except it should call parseFloat

[MurzNN]

In this logic I wanted to add support for , as decimal separator together with ., because it is popular in many countries
https://en.wikipedia.org/wiki/Decimal_separator#Countries_using_decimal_comma
So pasting something like 3,14159 should be converted to 3.14159 instead of 314159 or 3.
But this is debatable change, so now let's keep the previous logic to merge this, I've reverted this line to integer logic.