v1.8.0: deadlock fix, port various items from snapd

This release includes a fix for the "Pebble is unresponsive" deadlock issue described in #314, in addition to cross-porting various features from snapd, most notably the overlord/state changes in #344. Full list of changes below:

What's Changed

• ci(snap): cope with concurrent builds by @cjdcordeiro in #341
• tests(daemon): improve test coverage of notices API by @olivercalder in #346
• chore(state): cross-port latest changes from snapd's overlord/state by @dmitry-lyfar in #344
• fix(cmdstate): use imperative language and uppercase for task summary by @medvied in #348
• chore(deps): Bump critical dependencies. by @hpidcock in #353
• daemon: make ucrednetGet() return *ucrednet by @thp-canonical in #357
• fix(servstate): reduce scope of holding ServiceManager.planLock by @benhoyt in #355
• fix(servstate): don't hold both servicesLock and state lock at once by @benhoyt in #359

New Contributors

• @medvied made their first contribution in #348

Full list of commits: v1.7.0...v1.8.0