feat: add label slot

[schelmo]

Hi,

i added a label slot to replace the input with custom html.
also updated the CustomDropdown example to show the country flag of the current selected option.
vue-next-select in examples directory must be updated therefore after the next release?

[coveralls]

Pull Request Test Coverage Report for Build 1101882495

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 15 unchanged lines in 1 file lost coverage.
• Overall coverage increased (+0.5%) to 57.187%

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Files with Coverage Reduction	New Missed Lines	%
dist/vue-next-select.es.js	15	57.19%

Totals
Change from base Build 1101727014:	0.5%
Covered Lines:	330
Relevant Lines:	525

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💛 - Coveralls

[soc221b]

Thank you for the contribution ❤️ .

No, the version of vue-next-select in examples directory should be automatically bumped by action 😄 .

Still have requests

[soc221b]

❤️