[v2] Docs rewrite rules

[aemous]

Description of changes:

• Created a custom Sphinx extension that generates a package.redirects.conf file containing Apache redirect rules for each documented service operation supported by the AWS CLI v2.
• Added the extension to the Sphinx conf.py file's extensions list so that it is invoked during executions of Sphinx build.

Description of tests:

• Manually generated the docs locally following our documentation (i.e. via make all).
  • Verified a package.redirects.conf file is generated to our build output folder /doc/build/html/package.redirects.conf.
  • Verified that each RewriteRule in the generated file should be there, by verifying the exact same rule is generated in the corresponding file for AWS CLI v1 (using the test script below).
  • Verified that no RewriteRules that should be generated are excluded, by verifying that each rule generated for AWS CLI v1 is present in the generated file (using the test script below).
• Ran and passed all of our test suites (unit, functional, integration, etc.).
• Ran the AWS CLI v2 build CI/CD pipeline and verified that the generated documentation artifact contains the generated package.redirects.conf in its root.

Test script used for verifying correctness of the generated file's contents:

import os

if __name__ == '__main__':
    out_path = os.path.join(os.path.abspath('.'), 'package.redirects.conf') # path to CLI v2 generated file
    out_path2 = os.path.join(os.path.abspath('.'), 'package.redirects.conf.comp') # path to CLI v1 file (for comparison)

    def produce_lines(file_path, index):
        with open(file_path, 'r') as out_file:
            new_lines = []
            line_num = 0
            for line in out_file:
                line_num += 1
                if line_num < 3:
                    continue
                str = line[index:].split()[0]
                new_lines.append(str)
        return new_lines

    lines1 = produce_lines(out_path, 24) # remove cliv2-specific prefix from string for comparison
    lines2 = produce_lines(out_path2, 27) # remove cliv1-specific prefix from string for comparison
    print(f'Number of CLIv2 rewrite rules: {len(lines1)}')
    print(f'Number of CLIv1 rewrite rules: {len(lines2)}')
    lines1_cpy = list(lines1)
    lines2_cpy = list(lines2)

    for line in lines1:
        if line in lines2_cpy:
            lines2_cpy.remove(line)

    for line in lines2:
        if line in lines1_cpy:
            lines1_cpy.remove(line)

    print(f'RewriteRules in cliv1 not in cliv2: {lines2_cpy}')
    print(f'RewriteRules in cliv2 not in cliv1: {lines1_cpy}')

After generating the redirects file via make all using the extension added in this PR, I observed the following output from running this script:

Number of CLIv2 rewrite rules: 17036
Number of CLIv1 rewrite rules: 17045
RewriteRules in cliv1 not in cliv2: ['pinpoint-sms-voice-2018-09-05/CreateConfigurationSet$', 'pinpoint-sms-voice-2018-09-05/CreateConfigurationSetEventDestination$', 'pinpoint-sms-voice-2018-09-05/DeleteConfigurationSet$', 'pinpoint-sms-voice-2018-09-05/DeleteConfigurationSetEventDestination$', 'pinpoint-sms-voice-2018-09-05/GetConfigurationSetEventDestinations$', 'pinpoint-sms-voice-2018-09-05/ListConfigurationSets$', 'pinpoint-sms-voice-2018-09-05/SendVoiceMessage$', 'pinpoint-sms-voice-2018-09-05/UpdateConfigurationSetEventDestination$', 'pinpoint-sms-voice-2018-09-05/(.*)$']
RewriteRules in cliv2 not in cliv1: []

• 8 of the 9 RewriteRules being flagged as being in v1 that are NOT in v2 can be explained by the fact that cliv1 generates duplicate rules of all operations under the service pinpoint-sms-voice, since it is a copy of the service sms-voice. These 8 are all of the duplicate modeled operations.
• The remaining RewriteRule being flagged as being in v1 that is NOT in v2 is pinpoint-sms-voice-2018-09-05/ListConfigurationSets$. This can be explained by the fact that the CLI v2 does not currently support this operation as of testing.

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