feat(theme:title): add selector property

[cipchk]

• close refactor: TitleService ng-alain#2231

PR Checklist

Please check if your PR fulfills the following requirements:

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

PR Type

What kind of change does this PR introduce?

[ ] Bugfix
[x] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Build related changes
[ ] CI related changes
[ ] Documentation content changes
[ ] Application (the showcase website) / infrastructure changes
[ ] Other... Please describe:

What is the current behavior?

Issue Number: N/A

What is the new behavior?

Does this PR introduce a breaking change?

[ ] Yes
[x] No

Other information

[ng-alain-bot]

Preview is ready!

[codecov]

Codecov Report

Merging #1487 (bc9da75) into master (d8efc02) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #1487   +/-   ##
=======================================
  Coverage   95.37%   95.38%           
=======================================
  Files         270      270           
  Lines        8436     8443    +7     
  Branches     1575     1575           
=======================================
+ Hits         8046     8053    +7     
  Misses        300      300           
  Partials       90       90           

Impacted Files	Coverage Δ
packages/theme/src/services/title/title.service.ts	100.00% <100.00%> (ø)

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