feat(no-redundant-notify): also catch unsubscribe

[JasonWeinzierl]

Adds unsubscribe to the logic that guards against sending redundant notifications.

unsubscribe is already discouraged by no-subject-unsubscribe, but the subscriber argument of new Observable could also be affected. Also, unsubscribe technically isn't a "notification", but it's a rare enough use case that it's probably not worth splitting into a separate rule.

Resolves #107

[github-actions]

LCOV of commit bf24cd6 during .github/workflows/ci.yml #347

Summary coverage rate:
  lines......: 96.7% (4250 of 4396 lines)
  functions..: 96.1% (270 of 281 functions)
  branches...: 91.1% (932 of 1023 branches)

Files changed coverage rate:
                                         |Lines       |Functions  |Branches    
  Filename                               |Rate     Num|Rate    Num|Rate     Num
  =============================================================================
  src/rules/no-redundant-notify.ts       |84.4%     90| 100%     4|53.3%     15