[EuiBadge][EuiBetaBadge] Clarify use of badges

[ryankeairns]

Problem

What started as a bespoke badge for labeling new capabilities (e.g. Beta, Tech preview), EuiBetaBadge has grown to include deprecated capabilities (internal guidelines). Further, there seem to be cases of potential misuse where a regular EuiBadge should be used instead of the beta badge.

Goal

Clarify the use of badges for these use cases and apply them consistently across our products.

Proposal

Make the EuiBetaBadge more opinionated in the following ways:

1. Reserve hollow and accent for new capabilities
2. Reserve subdued and warning for deprecated capabilities
3. Remove icon-only variations for subdued and warning

Visually, that would look like:

Note about cleanup

This would very likely entail changing existing instances of subdued EuiBetaBadge either to another color (if denoting a new capabilitye) or to use EuiBadge instead (not related to new or deprecated capabilities).

cc:/ @jovana-andjelkovic

[ryankeairns]

The docs example was updated although the component still does not restrict combinations.