feat: add support for removing a single request cache by key(#515)

[smnsht]

New function 'deleteRequestsCache'

resolves #515

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/ngneat/elf/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
[ ] Other... Please describe:

What is the current behavior?

@ngneat/elf-requests does not support removing a single request cache by key

Issue Number: #515

What is the new behavior?

New function 'deleteRequestsCache' can invalidate in cache a single key or list of keys

Does this PR introduce a breaking change?

[ ] Yes
[x] No

Other information

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