Release version 0.18.0

Changelog

• db186c2 adjust exported error messages
• 479bf34 cli: add support for encrypted private keys
• edeadf3 client: add Enclave type
• da7f9a8 include client IP address in audit log
• 7457bf3 kes: add Status API to client SDK
• 90a133d kestest: add new API tests
• 4073c5f key: remove Manager and export Cache
• e451721 move policy assignment to v1/policy API
• f5171cf remove HTTP trailers from v1/identity/list API
• 4a504d8 remove HTTP trailers from v1/identity/list API
• 74cf93c remove HTTP trailers from v1/key/list API
• 2d746fc remove support for go1.16, enable gofumpt
• 8a93db9 rename /v1/identity/forget API to /v1/identity/delete
• 5d0a857 simplify error and audit log API
• 1bc46ac sys: add minimal multi-tenancy support via Enclaves (#183)
• 816d343 update container base-image ubi-8.5
• 53fd3b7 use iterator pattern for policy API