build(deps): upgrade Angular dependencies to v15

[un1c0rnr1d3r]

Please check if the PR fulfills these requirements

• The commit message follows our guidelines: https://github.com/moribvndvs/ng2-idle/blob/master/CONTRIBUTING.md#pr
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

What kind of change does this PR introduce? (check one with "x")

[ ] Bugfix
[ ] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[X] Build related changes
[ ] CI related changes
[ ] Other... Please describe:

What is the current behavior? (You can also link to an open issue here)
Angular v14 dependencies are in use.

What is the new behavior?
Angular dependencies have been upgraded to v15.

Does this PR introduce a breaking change? (check one with "x")

[ ] Yes
[X] No

If this PR contains a breaking change, please describe the impact and migration path for existing applications: ...

Other information:

[coveralls]

Coverage: 100.0%. Remained the same when pulling f73e19e on upgrade-deps-angular-15 into 2458281 on master.

[moribvndvs]

@un1c0rnr1d3r The peer dependencies for core and keepalive package.json still have >=9.0.0. Is this update safe for projects that targets those versions still, or do we need to bump these requirements up?

If no, then I can just release this as another patch to v12. If yes, then we'll need to set the minimum version and add that as a breaking change, moving ng-idle to 13.

Missed potential peerDependencies issue

[un1c0rnr1d3r]

@moribvndvs Technically, Angular does not support building an application using a version older than the one the library was built with. However, I think this release should continue to work (albeit officially unsupported) with Angular v9+.