PurlDB: purl2sym Data collection Batch5

[pombredanne]

Here we add purl2sym support for a list of PURLs listed below.

1. [x] Add support in FetchCode and PurlDB
2. [x] Test of end-to-end support in the PurlDB

The PURLs are:

• [x] pkg:gnu/libiconv
• [x] pkg:generic/toybox
• [x] pkg:generic/dropbear
• [x] pkg:github/python/cpython
• [x] pkg:generic/syslinux
• [x] pkg:github/rpm-software-management/rpm
• [x] pkg:github/pupnp/pupnp
• [x] pkg:generic/miniupnpc
• [x] pkg:generic/miniupnpd
• [x] pkg:generic/minissdpd
• [x] pkg:github/google/brotli
• [x] pkg:github/libbpf/bpftool
• [x] pkg:github/sqlite/sqlite
• [x] pkg:generic/barebox
• [x] pkg:github/nixos/nix
• [x] pkg:generic/linux (this was moved to batch 6 and back here as this was pending resolution of https://github.com/nexB/scancode.io/issues/1143 and https://github.com/nexB/purldb/issues/362 before we could do end-to-end test for linux.)

[keshav-space]

Completed in:

• https://github.com/nexB/fetchcode/pull/112
• https://github.com/nexB/fetchcode/pull/115
• https://github.com/nexB/purldb/pull/360

The simple way to test this is to follow the below steps after installing PurlDB (https://github.com/nexB/purldb?tab=readme-ov-file#installation):

1. Go to /api/collect/ add PURL for indexing. ex: /api/collect/?purl=pkg:gnu/libiconv@1.17&addon_pipelines=collect_symbols_ctags
2. Once the indexing has completed go to /api/resources/and filter out resource based on PURL to see the symbols for each resource in extra_data field. ex: /api/resources/?purl=pkg:gnu/libiconv@1.17

[!TIP] Follow this tutorial to index the symbols and strings literals for a PURL/Package using various different addon pipelines. https://aboutcode.readthedocs.io/projects/PURLdb/en/latest/how-to-guides/tutorial_symbol_and_string_collection.html