Obfuscate secret token after removing Fleet's ability to read secrets

[simitt]

Fleet/Kibana now supports secrets in the Kibana UI, as described in https://github.com/elastic/kibana/issues/154715#issuecomment-1678430435. We should set secret: true for secret-token in the apm package (https://github.com/elastic/apm-server/blob/main/apmpackage/apm/manifest.yml#L52).

[sorenlouv]

@gbamparop Do you think this is something we can do in 8.11? I'm very doubtful so I'd suggest pushing this to 8.12 (Kibana issue for context)

[gbamparop]

@gbamparop Do you think this is something we can do in 8.11? I'm very doubtful so I'd suggest pushing this to 8.12 (Kibana issue for context)

I agree, let's plan it for 8.12 if it's not urgent.

[sorenlouv]

@gbamparop Do you think this is something we can do in 8.11? I'm very doubtful so I'd suggest pushing this to 8.12 (Kibana issue for context)

I agree, let's plan it for 8.12 if it's not urgent.

It's been unencrypted for years so I don't see the urgency.