Snapshot management small fixes

[bowenlan-amzn]

Signed-off-by: bowenlan-amzn bowenlan23@gmail.com

Description

• Notification integration is added
• Remove timestamp input from create policy page, because we haven't finalized the design for it before release 2.1
• Make custom configuration help text in create repo flyout more prominent
• Tune the snapshot table to have more space for showing snapshot name which could be long
• Show notification channel name and type instead of id in policy detail page
• Add snapshot management to left nav bar under opensearch plugins, in the future, these may move to management section.

Issues Resolved

[List any issues this PR will resolve]

Check List

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[codecov-commenter]

Codecov Report

Merging #208 (b13df42) into main (f08cbe2) will decrease coverage by 0.24%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main     #208      +/-   ##
==========================================
- Coverage   51.84%   51.59%   -0.25%     
==========================================
  Files         182      183       +1     
  Lines        5750     5795      +45     
  Branches      924      933       +9     
==========================================
+ Hits         2981     2990       +9     
- Misses       2548     2584      +36     
  Partials      221      221              

Impacted Files	Coverage Δ
...ards-plugin/public/services/NotificationService.ts	70.00% <0.00%> (-30.00%)	⬇️
...hotPolicy/components/CronSchedule/CronSchedule.tsx	11.76% <0.00%> (-0.24%)	⬇️
.../CreateRepositoryFlyout/CreateRepositoryFlyout.tsx	12.69% <0.00%> (-0.21%)	⬇️
...ement-dashboards-plugin/public/pages/Main/Main.tsx	7.54% <0.00%> (-0.15%)	⬇️
...s/containers/SnapshotPolicies/SnapshotPolicies.tsx	7.51% <0.00%> (-0.12%)	⬇️
...ndex-management-dashboards-plugin/public/plugin.ts	0.00% <0.00%> (ø)
...gement-dashboards-plugin/public/utils/constants.ts	100.00% <0.00%> (ø)
...gin/public/pages/CreateSnapshotPolicy/constants.ts	0.00% <0.00%> (ø)
...pages/Snapshots/containers/Snapshots/Snapshots.tsx	4.59% <0.00%> (ø)
...ents/CreateSnapshotFlyout/CreateSnapshotFlyout.tsx	12.98% <0.00%> (ø)
... and 4 more

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