Chore: Modernize docs configuration for Python 3.12+

Chore: Modernize docs configuration for Python 3.12+

Remove broken/outdated Python modules that are incompatible with modern
Python versions. Update .readthedocs.yaml to use ubuntu-24.04 and Python
3.13. Modernize tox.ini (pin basepython to 3.12, use local constraints
instead of remote URLs, remove echo commands). Refresh docs/conf.py to
remove sphinxcontrib-swaggerdoc. Add etc/upper-constraints.onap.txt from
the doc repo.

Replace swaggerv2doc directives with openapi directives in the SLI API
docs (asdcApi, lcm, dataChange, sliapi) since sphinxcontrib-swaggerdoc
has been removed and sphinxcontrib-openapi is the replacement.

Fix JSON Pointer resolution errors in auto-generated Swagger specs
(asdc-api.json, lcm.json) caused by forward slash (/) characters in
definition key names. Replace / with . in definition keys and $ref
values per RFC 6901. Add stub definitions for dangling references
(Optional.empty and 18 missing (config)/(operational) schemas in
asdc-api.json) that were omitted by the YANG code generator.

Update JIRA and Confluence URLs from jira.onap.org/wiki.onap.org to
lf-onap.atlassian.net equivalents to fix linkcheck failures caused by
the migration to Atlassian Cloud. Fix malformed RST label definition
for secissues (had trailing space before colon).

Fix broken git clone URLs in docs/sli/build.rst (http:// to https://).
Add linkcheck_ignore patterns for Gerrit anonymous clone URLs, defunct
Cloudify docs, and archived docs.onap.org release submodule paths.

Removed modules: sphinxcontrib-swaggerdoc, six.

Issue-ID: CIMAN-33
Change-Id: I6b0f713186bc1f7c08aad3d29871350ed9423a5f
Signed-off-by: Matthew Watkins <mwatkins@linuxfoundation.org>