docs: add Bitnami (#5078)

* docs: add Bitnami

Signed-off-by: knqyf263 <[email protected]>

* docs: add a Debian link

Signed-off-by: knqyf263 <[email protected]>

---------

Signed-off-by: knqyf263 <[email protected]>

Author: knqyf263

docs/docs/coverage/os/bitnami.md

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+# Bitnami Images
+
+!!! warning "EXPERIMENTAL"
+    Scanning results may be inaccurate.
+
+While it is not an OS, this page describes the details of the [container images provided by Bitnami](https://github.com/bitnami/containers).
+Bitnami images are based on [Debian](debian.md).
+Please see [the Debian page](debian.md) for OS packages.
+
+Trivy supports the following scanners for Bitnami packages.
+
+|    Scanner    | Supported |
+| :-----------: | :-------: |
+|     SBOM      |     ✓     |
+| Vulnerability |     ✓     |
+|    License    |     ✓     |
+
+The table below outlines the features offered by Trivy.
+
+|               Feature                | Supported |
+| :----------------------------------: | :-------: |
+|       Unfixed vulnerabilities        |     -     |
+| [Dependency graph][dependency-graph] |     -     |
+
+## SBOM
+Trivy analyzes the SBOM information contained within the container images provided by Bitnami.
+The SBOM files are located at `/opt/bitnami/<component>/.spdx-<component>.spdx`.
+
+## Vulnerability
+Since Bitnami has its [own vulnerability database][vulndb], it uses these for vulnerability detection of applications and packages distributed by Bitnami.
+
+!!! note
+    Trivy does not support vulnerability detection of independently compiled binaries, so even if you scan container images like `nginx:1.15.2`, vulnerabilities in Nginx cannot be detected.
+    This is because main applications like Nginx are [not installed by the package manager](https://github.com/nginxinc/docker-nginx/blob/321a13a966eeff945196ddd31a629dad2aa85eda/mainline/debian/Dockerfile).
+    However, in the case of Bitnami images, since these SBOMs are stored within the image, scanning `bitnami/nginx:1.15.2` allows for the detection of vulnerabilities in Nginx.
+
+### Fixed Version
+Trivy refers to the [Bitnami database][vulndb]. Please note that these may differ from the upstream fixed versions.
+
+### Severity
+Similar to Fixed versions, it follows Bitnami's vulnerability database.
+
+### Status
+Trivy supports the following [vulnerability statuses] for Bitnami packages.
+
+|       Status        | Supported |
+| :-----------------: | :-------: |
+|        Fixed        |     ✓     |
+|      Affected       |     ✓     |
+| Under Investigation |           |
+|    Will Not Fix     |           |
+|    Fix Deferred     |           |
+|     End of Life     |           |
+
+
+
+## License
+If licenses are included in the SBOM distributed by Bitnami, they will be used for scanning.
+
+[dependency-graph]: ../../configuration/reporting.md#show-origins-of-vulnerable-dependencies
+
+[vulndb]: https://github.com/bitnami/vulndb
+[vulnerability statuses]: ../../configuration/filtering.md#by-status