out_azure_blob: add support for log_key

[adityasoni99]

Is your feature request related to a problem? Please describe.
By default, the whole log record gets sent to azure_blob.

If you specify a key name with "log_key" option in the azure_blob output plugin configuration, then only the value of that key
should be sent to azure_blob.

Reference PR for out_s3 plugin: #3668

Record without log_key

{"date":"2021-06-16T19:56:28.441428Z","log":"Pi is roughly 3.141605814119434"}

Record with log_key log

Pi is roughly 3.141605814119434

[github-actions]

This issue is stale because it has been open 90 days with no activity. Remove stale label or comment or this will be closed in 5 days. Maintainers can add the exempt-stale label.

[adityasoni99]

Work is being done on the PR

[github-actions]

This issue is stale because it has been open 90 days with no activity. Remove stale label or comment or this will be closed in 5 days. Maintainers can add the exempt-stale label.

[github-actions]

This issue was closed because it has been stalled for 5 days with no activity.

[overmeulen]

Hello,
I have a similar requirement.
@tomekwilk are you still working on this ?

[tomekwilk]

There are 2 open PRs for this issue. fluent-bit-docs #1540 is approved and fluent-bit #9791 is waiting for review.