Angular i18n directives should treat as HTML only values that are marked as such

[azasypkin]

Currently all values that are passed via i18n-values directive are treated as HTML. Even though values are sanitized and don't introduce a security risk it still may have undesired effect for values that may look like HTML (e.g. contains < or >), but in reality aren't.

Ideally we should explicitly mark values that should be treated as HTML (e.g. with html_ prefix like was discussed in #23684), the rest should be treated as plain text.

In the scope of this issue we should audit all existing cases where we use i18n-values and make sure we use HTML only where it's really needed.

[elasticmachine]

Pinging @elastic/kibana-platform