feat: enable the SSL feature in DP by default

[membphis]

APISIX version: 2.1

It not a good idea to disable the SSL feature by default, and it is not easy to enable this feature.
we should enable it by default.

Then we can use the placeholder certificate, and then APISIX can start normally.

[membphis]

@Yiyiyimu do you have time handle this issue?

[Yiyiyimu]

Hi @membphis So do we use the original test certificate as the placeholder? If that is the case, I think we could directly revert the whole PR.

[membphis]

we can copy the test certificate file as the placeholder. and the file name should contain the keyword placeholder.

so we do not need to revert the whole PR.

[Yiyiyimu]

Got it thx! Do we still put the copied certificates in conf/cert?

[membphis]

Got it thx! Do we still put the copied certificates in conf/cert?

confirm with this