[Fleet] Unified integrations follow up tech debt

[joshdover]

Follow up tech debt work from #93084

• NS Integrations results provider: avoid throwing when the user does not have superuser permissions #111094
• Missing logos on the integrations page #116975
• Add API docs for custom_integrations (prefer to wait on this after this stabilizes)
• Rename custom_integrations-plugin to integrations
• Improve icon-typing
• Internationalize category labels
• [Fleet] Enterprise Search plugins are not included in the total count of custom integrations on CI #115108
• On Clicking 'Add data' link under Analytics tab appropriate message is not displayed when user have no access to Integrations. #116265
• [Fleet] Remove short-term solution to detecting ESS cname & URL #120497

[elasticmachine]

Pinging @elastic/fleet (Team:Fleet)

[jen-huang]

@joshdover I added #116265 to this list, I recall seeing related fix(es) but wasn't sure if this was captured elsewhere.