docs(samples): Add filtered listing samples

[gwhitehawk]

Thank you for opening a Pull Request! Before submitting your PR, there are a few things you can do to make sure it goes smoothly:

• [x ] Make sure to open an issue as a bug/issue before writing your code! That way we can discuss the change, evaluate designs, and agree on the general idea
• [ x] Ensure the tests and linter pass
• [ x] Code coverage does not decrease (if any source code was changed)
• [ x] Appropriate docs were updated (if necessary)

Fixes #208 🦕

[snippet-bot]

Here is the summary of changes.

You are about to add 2 region tags.

• samples/snippets/list_secret_versions_with_filter.py:21, tag secretmanager_list_secret_versions_with_filter
• samples/snippets/list_secrets_with_filter.py:20, tag secretmanager_list_secrets_with_filter

---

This comment is generated by snippet-bot.
If you find problems with this result, please file an issue at:
https://github.com/googleapis/repo-automation-bots/issues.
To update this comment, add snippet-bot:force-run label or use the checkbox below:

• Refresh this comment

[busunkim96]

Note: Adding the CLI is not encouraged or required, although it is a common pattern in many existing samples. Please keep this only if you think it is valuable for your users.

Code Snippet Style Guide

We expect that most developers will copy/paste the code from Code Snippets on cloud.google.com into their own codebase rather than attempt to run the Code Snippets as Sample Applications. Therefore, it's not critical that Code Snippets be runnable from the command line.

CLIs for Code Snippets have been very expensive to maintain in the past. We will not be creating new CLIs for Code Snippets and will be removing ones that exist.

[gwhitehawk]

Done.

[busunkim96]

Consider pre-filling with a valid filter_str = "..." to help users. The state:ENABLED passed in the test seems like a good option.

[gwhitehawk]

Done.

[google-cla]

All (the pull request submitter and all commit authors) CLAs are signed, but one or more commits were authored or co-authored by someone other than the pull request submitter.

We need to confirm that all authors are ok with their commits being contributed to this project. Please have them confirm that by leaving a comment that contains only @googlebot I consent. in this pull request.

Note to project maintainer: There may be cases where the author cannot leave a comment, or the comment is not properly detected as consent. In those cases, you can manually confirm consent of the commit author(s), and set the cla label to yes (if enabled on your project).

ℹ️ Googlers: Go here for more info.