[Files] Delay <Image/> blurhash reveal and handle blurhash errors

[Dosant]

Summary

Follow up to #145347
Needed for #81345
Partially fixes #145567

Two things:

• Handle errors related to blurhash loading. Make sure that the original image is loaded if blurhash is failed to generate src or failed to load
• Make blurhash appear after the delay. This is needed for better UX when the original image loads fast. Implemented using css animation where first part of the animation is a static state with opacity: 0, and then the image is revealed in the end. If the original image loads faster, then it appears instantaneously without the delay

[kibana-ci]

💛 Build succeeded, but was flaky

• Buildkite Build
• Commit: 0bc6499

Failed CI Steps

• x-pack/test/alerting_api_integration/security_and_spaces/group1/config.ts

Test Failures

• [job] [logs] x-pack/test/alerting_api_integration/security_and_spaces/group1/config.ts / alerting api integration security and spaces enabled Alerts - Group 1 alerts bulkDisableRules space_1_all_alerts_none_actions at space1 should handle disable alert request appropriately when consumer is "alerts"
• [job] [logs] x-pack/test/alerting_api_integration/security_and_spaces/group1/config.ts / alerting api integration security and spaces enabled Alerts - Group 1 alerts bulkDisableRules space_1_all_with_restricted_fixture at space1 should handle bulk disable of one rule appropriately based on id
• [job] [logs] x-pack/test/alerting_api_integration/security_and_spaces/group1/config.ts / alerting api integration security and spaces enabled Alerts - Group 1 alerts bulkDisableRules space_1_all_with_restricted_fixture at space1 should handle bulk disable of one rule appropriately based on id when consumer is the same as producer

Metrics [docs]

Page load bundle

Size of the bundles that are downloaded on every page load. Target size is below 100kb

id	before	after	diff
files	17.5KB	17.9KB	+462.0B

Unknown metric groups

ESLint disabled in files

id	before	after	diff
osquery	1	2	+1

ESLint disabled line counts

id	before	after	diff
enterpriseSearch	19	21	+2
files	2	4	+2
fleet	59	65	+6
osquery	109	115	+6
securitySolution	443	449	+6
total			+22

Total ESLint disabled count

id	before	after	diff
enterpriseSearch	20	22	+2
files	6	8	+2
fleet	68	74	+6
osquery	110	117	+7
securitySolution	520	526	+6
total			+23

To update your PR or re-run it, just comment with:
@elasticmachine merge upstream

[jloleysens]

Very nice enhancements, tested locally and it looks really good! Great job @Dosant !