[7.x] Improve xpack.security.session deprecation warnings

[watson]

This PR adds a title field to the two deprecation warnings and wraps all their text in i18n handlers. This brings them "up to speed" with the other deprecation warnings in this file.

Without the title field, a title would be generated automatically and it would not be possible to tell the two deprecations apart in the overview:

With this change, they now look like this:

[watson]

@elasticmachine merge upstream

[watson]

I just added the newly introduced level field so that we could get these to show up as warning instead of critical. This is how it looks:

Besides that, here's how the detailed message now looks with all the review comments taken into account:

[watson]

Now with proper quotes:

[kibanamachine]

💚 Build Succeeded

• continuous-integration/kibana-ci/pull-request
• Commit: 5e9a7f2
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Metrics [docs]

✅ unchanged

History

• 💚 Build #152504 succeeded e79875c
• 💚 Build #152489 succeeded 3dfe5ec
• 💔 Build #152472 failed 14e7e4e
• 💔 Build #152470 failed af9f7a2
• 💚 Build #151814 succeeded 1c455e9

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

cc @watson