instance: add migration System

[BeryJu]

For some upcoming changes like #1304 and #1249 we need the ability to migrate etcd data transparently and in a way that is compatible with other nodes in the cluster that might not be updated yet

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[codecov[bot]]

Codecov Report

Attention: Patch coverage is 65.02732% with 64 lines in your changes missing coverage. Please review.

Project coverage is 60.83%. Comparing base (78ad85f) to head (989e81c). Report is 2 commits behind head on main.

:x: We are unable to process any of the uploaded JUnit XML files. Please ensure your files are in the right format.

Files with missing lines	Patch %	Lines
pkg/storage/client.go	2.85%	33 Missing and 1 partial :warning:
pkg/instance/migrate/migrate.go	70.58%	14 Missing and 6 partials :warning:
pkg/instance/instance.go	55.55%	3 Missing and 1 partial :warning:
pkg/instance/migrate/inline_migration.go	82.35%	2 Missing and 1 partial :warning:
pkg/storage/trace/kv.go	90.62%	2 Missing and 1 partial :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #1312 +/- ## =========================================== + Coverage 21.90% 60.83% +38.93% =========================================== Files 233 107 -126 Lines 19910 6034 -13876 =========================================== - Hits 4361 3671 -690 + Misses 15099 2019 -13080 + Partials 450 344 -106 ```

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[codecov[bot]]

Bundle Report

Changes will increase total bundle size by 3.53MB (100.0%) :arrow_up::warning:, exceeding the configured threshold of 5%.

Bundle name	Size	Change
gravity-ui-esm	3.53MB	3.53MB (100%) :arrow_up::warning: