fix: support datadog plugin api key to allow for secret injection

[nitintecg]

What this PR does / why we need it:

Modified datadog_types.go file to support datadog plugin api key for allowing the value to take from secret.

Which issue(s) this PR fixes:

Fixes #1060

Does this PR introduced a user-facing change?

Additional documentation, usage docs, etc.:

[benjaminhuo]

@nitintecg Thanks for this PR.
You'll need to run the following to generate code and docs:

make manifests
make generate
make fmt
make vet
make docs-update

[nitintecg]

@benjaminhuo I'm getting below error while running make generate and make manifests commands

panic: runtime error: invalid memory address or nil pointer dereference [recovered]
        panic: runtime error: invalid memory address or nil pointer dereference

[benjaminhuo]

@benjaminhuo I'm getting below error while running make generate and make manifests commands

panic: runtime error: invalid memory address or nil pointer dereference [recovered]
        panic: runtime error: invalid memory address or nil pointer dereference

@wenchajun @wanjunlei This is an env issue?

[wenchajun]

You can check the go and controller_gem version,https://github.com/fluent/fluent-operator/blob/master/Makefile#L149

[nitintecg]

@wenchajun Thanks, it was go version issue and after installing proper go version it resolved my issue.
@benjaminhuo after running commands its generating docs for multine_types.go and rewritetag_types.go.
So its expected in this PR or should i exclude docs changes for multiline_types.go and rewritetag_types.go from my PR ?

[benjaminhuo]

@benjaminhuo after running commands its generating docs for multine_types.go and rewritetag_types.go.
So its expected in this PR or should i exclude docs changes for multiline_types.go and rewritetag_types.go from my PR ?

@nitintecg yeah, it's ok. Someone else forgets to generate docs for their PRs.
would you push your new changes?

[nitintecg]

@benjaminhuo i have added docs changes in this PR. Can you review ?

[fernandoataoldotcom]

@benjaminhuo i have added docs changes in this PR. Can you review ?

@nitintecg thanks a lot for working on this! We're adopting fluent bit and definitely need this capability.

[benjaminhuo]

@nitintecg would you help to resolve the conflicts?

[nitintecg]

@benjaminhuo , i tried resolving conflicts and was running commands for generating docs but while running make docs-update its giving below error.

Error while generating documentation: open ./docs/plugins/fluentbit/multilineparser/multilineparser.md: no such file or directory

Can you help me ?

[venkatamutyala]

@nitintecg The error you had might have been fixed around the time you had it. Please see: #1120

[benjaminhuo]

@nitintecg Thank you!