feat: support async search index create and update index settings

[Benj0s]

Pull request checklist

Please check if your PR fulfills the following requirements:

• [x] Build (npm run build) was run locally and any changes were pushed
• [x] Tests (npm run test) for the changes have been added (for bug fixes / features)
• [x] Docs (npm run doc) have been reviewed and added / updated if needed (for bug fixes / features)
• [x] PR title and git commit messages conform to the conventionalcommits specification

Pull request type

Please check the type of change your PR introduces:

• [ ] Bugfix
• [x] Feature
• [ ] Code style update (formatting, renaming)
• [ ] Refactoring (no functional changes, no api changes)
• [ ] Build related changes
• [ ] Documentation content changes
• [ ] Other (please describe):

What is the current behaviour?

Requests to create Search Indexes and update settings are currently done in a synchronous manner.

What is the new behaviour?

Support asynchronous Search Index create and settings update.

Does this introduce a breaking change?

• [ ] Yes
• [ ] No

[coveralls]

Pull Request Test Coverage Report for Build 3757170543

• 42 of 44 (95.45%) changed or added relevant lines in 4 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.2%) to 95.488%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/lib/model/SearchIndex.ts	22	24	91.67%
<!--	Total:	42	44	95.45%	-->

Totals
Change from base Build 2903125206:	-0.2%
Covered Lines:	960
Relevant Lines:	977

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💛 - Coveralls