chore: freeze Nebula version to v0.0.1

[mojomex]

Description

This PR freezes Nebula to version v0.0.1 (the current main branch, pre-merge of the current develop branch).
This is to prevent timing issues now and in the future when releasing breaking changes in Nebula.

🟢 The version referenced by this tag is the same one that is currently referenced by main, so there are no code changes.

Tests performed

Commit IDs are the same between the two refs:

Before:

~/autoware/src/sensor_component/external/nebula$ git branch
* main
~/autoware/src/sensor_component/external/nebula$ git rev-parse HEAD
18af521fc3a3ab1ce9c17ec94c2a0a8633317de4

After:

~/autoware/src/sensor_component/external/nebula$ git branch
* (HEAD detached at v0.0.1)
  main
~/autoware/src/sensor_component/external/nebula$ git rev-parse HEAD
18af521fc3a3ab1ce9c17ec94c2a0a8633317de4

Not applicable.

Effects on system behavior

Not applicable.

Interface changes

None.

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