Merge `mapping.example` and `network.settings` to one generalized settings file

We should merge these two files to one common settings file (e.g. `config.properties`/`settings.properties`). This reduces the number of files and provides us with a file to add more generalized configuration options.

### Required changes
- [ ] Replace `network.settings` and custom value mapping files with a `default.config` file
- Update the fetch-build-scan-data-cmdline-tool to read both network settings and custom value mappings from `default.config`.
- [ ] Replace `-m, --mapping-file` with `-z, --config-file`
- [ ] If the user provides a config file with `--config-file`, the settings override those in the default config.
- [ ] If a setting is in `--config-file`, then use it over all other settings
- [ ] If a setting does not exist in `--config-file`, but it does in `/config` and it is different from the universal default, then use the setting in `/config`.
- [ ] If a setting does not exist in the `--config-file` and it also does not exist in `/config`, then use a hard-coded default value (same default as what is used today).
- [ ] Output the config file at the start of the script run
- If a user provided a config file as an argument to the script, show the location of the user-provided config file.
- If no config file is specified by the user, output the location of the default config file.
- If the default config file has been deleted, show `` to indicate that no config file was applied.
- [ ] Include the "effective config" (the configuration after all overrides are resolved) in the experiment run directory.
- [ ] Update interactive mode
- [ ] For Gradle Exp 01, 02, 03, and Maven Exp 01, 02:
- [ ] Add collection step to ask for a config file that overrides the default config.
- Link to the section in the README that discusses configuration settings.
- [ ] For Gradle Exp 04, 05, and Maven Exp 03, 04:
- [ ] Replace the custom mapping file collection step with the collection step to ask for a config file that overrides the default config
- Link to the section in the README that discusses configuration settings.
- [ ] Remove the mapping file end-of-experiment explanation
- [ ] Include `-z` in the command to repeat the experiment.
- [ ] Update the Build Validation Script README files
- [ ] Group the mapping configuration and network settings under a Configuration section.
- The existing mapping and network setting sections are already listed together, so grouping them under a common Configuration section header should be okay.