fix(MemoryService): handle missing embedding model in memory configuration

[alephpiece]

What this PR does

Skips embeddingApiClient if the embedding model is not set. This could happen after switching from main to v2.

Before this PR:

After this PR:

Fixes #

Why we need it and why it was done in this way

The following tradeoffs were made:

The following alternatives were considered:

Links to places where the discussion took place:

Breaking changes

If this PR introduces breaking changes, please describe the changes and the impact on users.

Special notes for your reviewer

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Release note

[DeJeune]

LGTM