feat(no-unnecessary-collection): new rule

[JasonWeinzierl]

New rule to detect unnecessary usage of combineLatest, forkJoin, etc. where a collection (object or array) containing only a single observable is passed in. In these cases, combineLatest, etc. can be replaced with the single observable itself (after accounting for slight changes in output).

• This rule is added to the strict config.
• This rule does not include a fixer. A fixer could be implemented in future for merge, race, concat, and the overload of combineLatest that accepts an array.
• This rule does not support variable-length arrays and non-literal objects because their lengths are not guaranteed.
• Like most rules in this plugin, this rule does not support import aliases.

Resolves #39 and cartant#107 .

[github-actions]

LCOV of commit 8d11335 during .github/workflows/ci.yml #710

Summary coverage rate:
  lines......: 96.8% (4675 of 4829 lines)
  functions..: 96.3% (284 of 295 functions)
  branches...: no data found

Files changed coverage rate:
                                                                    |Lines       |Functions  |Branches    
  Filename                                                          |Rate     Num|Rate    Num|Rate     Num
  ========================================================================================================
  src/configs/strict.ts                                             | 2.3%     43| 0.0%     1|    -      0
  src/constants.ts                                                  | 0.0%     39|    -     0|    -      0
  src/index.ts                                                      | 0.0%    111|    -     0|    -      0
  src/rules/no-unnecessary-collection.ts                            | 4.5%     89| 0.0%     4|    -      0