feat: support gcp secret manager

[HuanXin-Chen]

Description

Many enterprises are utilizing cloud services from AWS and GCP, relying on the secret manager provided by these platforms to handle sensitive information. Integrating Apache APISIX with these secret managers can streamline the process of using sensitive information within APISIX, enabling users to manage and utilize cloud-stored sensitive data more conveniently, thus enhancing the overall security and usability of the system.

This PR has completed the support for GCP. It added the gcp.lua file to the original secret module, allowing users to store their secret information on GCP using the same reference method as before.

Checklist

• I have explained the need for this PR and the problem it solves
• I have explained the changes or the new features added to this PR
• I have added tests corresponding to this change
• I have updated the documentation to reflect this change
• I have verified that this change is backward compatible (If not, please discuss on the APISIX mailing list first)

[bzp2010]

Hi @kayx23

Please take a look at the documentation when you are free to see if there are any problems. 🫡

[HuanXin-Chen]

@bzp2010 @kayx23 @membphis @soulbird I have fixed some issues in the code. Please review it again when you have time. Thank you very much. 🙏

[bzp2010]

@HuanXin-Chen There were some failures in CI involving traffic-split3.t, no worries, just merge the master branch into your dev branch feat-gcp-secret, we've fixed that.

[HuanXin-Chen]

@bzp2010 @membphis @soulbird @kayx23 @shreemaan-abhishek
I think there's no problem in my pr. Some failures in CI are not related to my code, no worries, just retry may solve it.
Please review it when you're free. Only after this branch is merged can I proceed with the next step of work: #11576. Thank you!💗

[membphis]

LGTM, I mainly check the code style, doc and test case

[membphis]

LGTM, thx for your nice PR

[bzp2010]

Great job 🫡