[Cases] ServiceNow connectors UI changes

[semd]

Summary

Design improvements for #105440
Design ticket: https://github.com/elastic/stack-design-team/issues/109
Design Round 2: https://whimsical.com/servicenow-certification-ux-updates-FtUbWGLgxXppnWNSnwabwu

Note: this branch was created from #105440 branch so it contains all of its commits, though they are all already in master.

List of changes:

Connector's list:

• icon margin fixed

Edit connector form:

• Reduced distance between "Authenticate" title and info callout below

Update connector form:

• From a modal to a flyout (on top of "Edit connector" flyout)
• Warning flyout banner added

Dropdown deprecated connectors updated:

• icon margin fixed
• (deprecated) text added

Edit connector in case:

• warning color changed from danger to warning in the form callout
• connector icon moved from the left (EuiCard icon) to a new column aligned to the right

Connector's parameters form:

• After talking with the Alerting team the toggle/checkbox to update incident has been removed and got replaced by a text field (Correlation ID)
• Add Correlation display text field
• Remove observables fields from SIR (destination IP, source IP, malware hash and malware URL)

ITSM:

SIR:

Checklist

Delete any items that are not applicable to this PR.

• Any text added follows EUI's writing guidelines, uses sentence case text and includes i18n support
• Documentation was added for features that require explanation or tutorials
• Unit or functional tests were updated or added to match the most common scenarios
• Any UI touched in this PR is usable by keyboard only (learn more about keyboard accessibility)
• This was checked for cross-browser compatibility

For maintainers

• This was checked for breaking API changes and was labeled appropriately