Q1'21 handler maintenance

[calebhailey]

Repository Updates

• [x] Review any outstanding PRs/issues (are any easily addressable as part of this work?)
• [x] Switch default branch from master to main (ref https://github.com/github/renaming)

Module Updates

• [x] Update SDK, core, and all other modules with 'go get -u' (note: This may require some manual cleanup)
• [x] Cleanup with 'go mod tidy'

README Updates

• [x] Add note on templates and link to docs, when needed
• [x] Ensure help output is current
• [x] Caveat on using check annotations (ref https://github.com/sensu/sensu-pagerduty-handler/blob/master/README.md)
• [x] Make sure annotations are explained as overrides
• [x] Add table of environment variables available
• [x] Make sure layout matches current standard
• [x] Remove empty sections (e.g. Files, Additional Notes)

Golang version updates

• [x] Update go.mod to use 1.14
• [x] Update GitHub Actions (release and test) to use 1.14

GitHub Actions Updates

• [x] All have lint, test, and release actions
• [x] Add PR to lint and test actions on OSS handlers

Secrets update

• [x] For any password/token arguments, ensure 'Secret: true' is set

Code updates

• [x] Output supporting templates where it makes sense to (make sure to document in README)
• [x] Replace import of types with api/core/v2 and change types.Event references to corev2.Event
• [x] Run 'gofmt' on all source files

Output logging

• [x] Output logging information (e.g. any incident or job # created)

Release

• [x] Make sure Bonsai and GoReleaser configs are in sync and functioning Remove 32 bit macOS from Bonsai
• [x] Add any changes to CHANGELOG
• [x] Submit PR
• [ ] After merge, cut a new release
• [ ] In bonsai make sure the handler has the right tier (supported, enterprise)

Update curation(s)

• [ ] Update (or add new) curations to use new version/assets (add in template args if available)