Apps break on hosts where Splunk is configured to listen on IPv6 management port

Start in solnlib/splunkenv.py around get_splunkd_access_info(), especially the parsing of mgmtHostPort returned by get_conf_key_value(). Reproduce the failure with an IPv6 value such as [::]:8089 and verify that the management port is parsed correctly without breaking existing host:port values. The issue does not mention a specific test file, so add or locate coverage for these configurations before confirming the fix.

For apps which invoke the get_splunkd_access_info() function from splunkenv.py, errors are thrown when a host is configured to listen using IPv6 on the Splunk MGMT port.

This function uses get_conf_key_value() to read the value of mgmtHostPort from web.conf, and splits it based on the : delimiter in order to work out the value being used for the MGMT port on the current instance:

https://github.com/splunk/addonfactory-solutions-library-python/blob/ed4749fa4cca8caabd3cc90ddd56b4a19824751d/solnlib/splunkenv.py#L187-L191

This obviously breaks when encountering IPv6 addresses, which use : as a delimiter as part of the address. This also breaks when deploying a Splunk-recommended configuration to listen on IPv6 as well as v4, which looks like this:

mgmtHostPort = [::]:8089

This type of construct is interestingly not included in the spec file for web.conf but in the spec file for server.conf, which states:

You might need to change the mgmtHostPort setting in the web.conf file. Use '[::1]' instead of '127.0.0.1'.

I'm not quite sure what the best way of fixing this is. It seems like using : as a delimiter should still be possible, but the function should take care to ensure that where multiple : delimiters are present, the rightmost value is taken as the integer used for the port value.

An example error from a Splunkbase app breaking because of this bug:

12-11-2023 17:07:25.671 +0000 ERROR AdminManagerExternal [109547 TcpChannelThread] - Stack trace from python handler:\nTraceback (most recent call last):\n  File "/opt/splunk/lib/python3.7/site-packages/splunk/admin.py", line 108, in init_persistent\n    hand = handler(mode, ctxInfo, data)\n  File "/opt/splunk/etc/apps/TA-sandfly-security/bin/ta_sandfly_security/aob_py3/splunktaucclib/rest_handler/admin_external.py", line 95, in __init__\n    get_splunkd_endpoint(),\n  File "/opt/splunk/etc/apps/TA-sandfly-security/bin/ta_sandfly_security/aob_py3/splunktaucclib/rest_handler/admin_external.py", line 77, in get_splunkd_endpoint\n    splunkd_uri = get_splunkd_uri()\n  File "/opt/splunk/etc/apps/TA-sandfly-security/bin/ta_sandfly_security/aob_py3/solnlib/splunkenv.py", line 208, in get_splunkd_uri\n    scheme, host, port = get_splunkd_access_info()\n  File "/opt/splunk/etc/apps/TA-sandfly-security/bin/ta_sandfly_security/aob_py3/solnlib/splunkenv.py", line 188, in get_splunkd_access_info\n    port = int(host_port.split(":")[1])\nValueError: invalid literal for int() with base 10: ''\n