feat(ui): allow sharing pre-filled silence form via a link

[prymitive]

Fixes #1820

[prymitive]

Webpack bundle size diff

Total diff: -18.9 KB

M	build/static/js/6.23df5b6c.chunk.js	489.3 KB	467.6 KB	-21.6 KB

-	base64-js	1.3 KB		-1.3 KB
M	[no source]	13 KB	12.9 KB	-103 B
-	isarray	91 B		-91 B
-	ieee754	868 B		-868 B
-	buffer	19.2 KB		-19.2 KB
M	core-js	103.3 KB	103.3 KB	-4 B

M	build/static/js/8.b33418ef.chunk.js	46.4 KB	47.1 KB	+764 B

M	[no source]	11.4 KB	11.5 KB	+33 B
M	@FortAwesome	4.7 KB	5.4 KB	+731 B

M	build/static/js/16.9ea0cbd8.chunk.js	27.8 KB	29.2 KB	+1.5 KB

M	Components/SilenceModal/DateTimeSelect	7.5 KB	7.5 KB	+8 B
M	Components/SilenceModal	5.6 KB	7 KB	+1.4 KB
M	Components/SilenceModal/SilenceMatch	3.8 KB	3.9 KB	+22 B
M	[no source]	683 B	744 B	+61 B
M	Components/SilenceModal/AlertManagerInput	992 B	1012 B	+20 B

M	build/static/js/main.ccd01809.chunk.js	25.6 KB	26.1 KB	+523 B

M	Stores	14.7 KB	15.4 KB	+790 B
M	[no source]	1.8 KB	1.7 KB	-58 B
M	App.tsx	2.1 KB	2.2 KB	+60 B
M	AppBoot.js	890 B	674 B	-216 B
M	index.tsx	207 B	154 B	-53 B