Populate `Last Updated` on each page

[failfmi]

It would be nice to have the date when was the given page last updated. The field exists, it just has to be populated.

[heversonbr]

The issue here is that, the default docusaurus plugin (i.e.,plugin-content-docs) that captures the 'date' and 'author' information for doc file uses git log command to retrieve these information when the options: showLastUpdateAuthor and showLastUpdateTime are set to true.

file: node_modules/@docusaurus/utils/lib/gitUtils.js

function getFileCommitDate(file, { age = 'oldest', includeAuthor = false, }) {
    if (!shelljs_1.default.which('git')) {
        throw new GitNotFoundError(`Failed to retrieve git history for "${file}" because git is not installed.`);
    }
    if (!shelljs_1.default.test('-f', file)) {
        throw new Error(`Failed to retrieve git history for "${file}" because the file does not exist.`);
    }
    const args = [
        `--format=%ct${includeAuthor ? ',%an' : ''}`,
        '--max-count=1',
        age === 'oldest' ? '--follow --diff-filter=A' : undefined,
    ]
        .filter(Boolean)
        .join(' ');
    const result = shelljs_1.default.exec(`git log ${args} -- "${path_1.default.basename(file)}"`, {  

As the spec website is a submodule of the spec documentation and the source files are copied to the docusaurus's to 'src/docs' directory at building time, the default plugin cannot get the required information from the local website git repo (because the directory is ignored by the local .gitignore). A potential solution I see here is to re-write a new plugin for docusaurus to grab the information from the spec-repo by using git API instead of git log.